HR: 13:55h
AN: T42D-02    [PDF]
TI: Effects of Temperature and Water on Deformation Microstructures of Olivine
AU: * Katayama, I
EM: ikuo.katayama@yale.edu
AF: Yale University, Department of Geology & Geophysics, New Haven, CT 06520 United States
AU: Jiang, Z
EM: zhenting.jiang@yale.edu
AF: Yale University, Department of Geology & Geophysics, New Haven, CT 06520 United States
AU: Karato, S
EM: shun-ichiro.karato@yale.edu
AF: Yale University, Department of Geology & Geophysics, New Haven, CT 06520 United States
AB: Recent studies in our laboratory have shown that water and stress have important effects on deformation microstructures of olivine including lattice preferred orientation and recrystallized grain-size (Jung and Karato, 2001a,b). These findings provide us with different interpretations of the geodynamic significance of seismic anisotropy, particularly in subduction zones. However, these initial studies were limited to a narrow temperature range ($\sim$1500-1600K). Theoretical considerations suggest that in addition to water content and stress, temperature is likely to modify these microstructures. Temperatures in some parts of subduction zone upper mantle are likely significantly lower than $\sim$1500 K. Consequently, it is crucial to extend these previous studies to lower temperatures and compare these results with microstructures of naturally deformed peridotites from collision zones which were likely deformed at low temperature conditions. We conduct deformation experiments in simple shear at lower-temperature (to 1273 K). An olivine single crystal was sandwiched between alumina pistons cut at $45^o$ from the compression direction, and surrounded by a mixture of talc and brucite that acts as a water source. Shear strain was measured by the rotation of a strain marker, and the microstructures of olivine samples were investigated by a scanning electron microscope with an electron backscatter diffraction (EBSD) technique. Even at a temperature as low as $\sim$1273 K, samples were totally recrystallized at small strain ($\sim$0.8). The recrystallized olivine grains show a fabric which is different from any of the known fabrics. We tentatively interpret this as caused by the combination of inherited fabric and deformation- (+ recrystalllization-) induced fabric involving the activity of the b=[001]. The details of fabrics and its variation with temperature, stress and water content will be reported together with a comparison with the fabrics in naturally deformed peridotites under low temperature (and "wet" ?) conditions.
DE: 3904 Defects
DE: 8030 Microstructures
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8160 Rheology--general
DE: 8164 Stresses--crust and lithosphere
SC: Tectonophysics [T]
MN: 2003 Fall Meeting