HR: 0800h
AN: T21A-0514    [Abstracts]
TI: Eclogite Rheology and Fabrics at High Temperature and High Pressure
AU: * Zhang, J
EM: jzhan002@student.ucr.edu
AF: IGPP/Dept. of Earth Sciences, Univ. of California, Riverside, CA 92521 United States
AU: Green, H W
EM: hgreen@mail.ucr.edu
AF: IGPP/Dept. of Earth Sciences, Univ. of California, Riverside, CA 92521 United States
AB: Eclogite plays an important role for mantle convection and geodynamics in subduction zones. An improved understanding of processes in the deeper levels of subduction zones and collision belts requires information on eclogite rheology. However, the deformation processes and associated fabrics in eclogite are not well understood. Incompatible views of deformation mechanism have been proposed for both garnet and omphacite. We investigated here the high temperature deformation behavior of eclogite reconstituted from powders of 50% garnet, 40% omphacite, 10% quartz and trace rutile at temperatures of 1000-1600 K, a confining pressure of 2.5-3.5 GPa, and strain rates of 10$^{-4}$/s to 10$^{-5}$/s. We obtained a power-law creep for the high temperature deformation of eclogite with n=3.4$\pm$0.5 and Q=420$\pm$70 KJ/mol. Microscopic fabrics of these experimental eclogites were analyzed with the Electron Back Scattered Diffraction (EBSD) technique. Our results show that: (I) Garnet displays complex pole figures with random distributions of misorientation angles in good agreement with rigid round garnets; (II) Omphacite shows a pronounced S-type crystallographic preferred orientation characterized by [001] axis forming a well-defined girdle near parallel to the foliation and poles of (010) normal to the foliation; suggesting a dislocation creep mechanism. Further investigation into the water effects on eclogite show: (I) Hydroxyl content does not induce a change in the microfabric of omphacite; (II) Grain boundary processes dominate the deformation of garnet under high water fugacity conditions, yielding a random crystallographic preferred orientation similar to that of nondeforming garnet. These results are remarkably similar to observations from deformed eclogites in nature.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8160 Rheology--general
DE: 5120 Plasticity, diffusion, and creep
DE: 3902 Creep and deformation
DE: 3924 High-pressure behavior
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting