HR: 0800h
AN: T11B-1253    [Abstracts]
TI: Deformation Experiments on Polycrystalline Mg2SiO4-Ringwoodite Using the Deformation-DIA and Monochromatic X-Ray Diffraction
AU: * Nishiyama, N
EM: nishiyama@cars.uchicago.edu
AF: Center for Advanced Radiation Sources, Univ. Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 United States
AU: Wang, Y
EM: wang@cars.uchicago.edu
AF: Center for Advanced Radiation Sources, Univ. Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 United States
AU: Uchida, T
EM: uchida@cars.uchicago.edu
AF: Center for Advanced Radiation Sources, Univ. Chicago, 5640 S. Ellis Ave., Chicago, IL 60637 United States
AU: Irifune, T
EM: irifune@dpc.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime Univ., Matsuyama, 790-8577 Japan
AU: Ischia, G
EM: ischiagloria@berkeley.edu
AF: Dept Earth Planetary Science, Univ. California, Berkeley, CA 94720 United States
AU: Wenk, H
EM: wenk@seismo.berkeley.edu
AF: Dept Earth Planetary Science, Univ. California, Berkeley, CA 94720 United States
AB: Deformation experiments under controlled differential stress and strain rates were carried out on ringwoodite (Mg2SiO4) samples using the deformation-DIA (D-DIA) with monochromatic X-ray diffraction. Samples (0.8 mm dia., 1.2 mm long) were sintered polycrystalline rocks, synthesized at 20GPa and 1523K at Geodynamic Research Center (Ehime Univ., Japan), with an average grain size of $<$10$\mu$m and no observable preferred orientation. Each sample was surrounded by a BN sleeve, with two fully densified alumina pistons above and below as deformation pistons. Two Au foils were put between the sample and the pistons as strain markers. Monochromatic X-rays with an energy of 65 keV ($\lambda$=0.19$\AA$) were used. Two-dimensional (2-D) diffraction patterns were repeatedly collected during the deformation process using an X-ray CCD. Differential lattice strains were determined based on the distortion of the Debye rings. The differential stresses were calculated from the lattice strain using single crystal elastic constants. Total sample lengths were determined by radiography. Multiple stress-strain curves (compression and extension) were obtained at various temperatures at pressures from 4 to 10 GPa, with the total axial strain up to 22$%$. Our results show that (1) at room T ringwoodite deforms in the ductile regime, (2) the strength of ringwoodite increases with P and decreases with T, (3) ringwoodite exhibits modest strain hardening (many discrepancies in strength measurements previously reported, where no total strain information could be obtained, can be reconciled by taking into account the strain dependence on strength), and (4) ringwoodite develops strong lattice preferred orientation even at modest strains, which was clearly observed as intensity variation with angles along Debye rings. At 5-10 $%$ axial strain, a strong texture had already developed with the 110 poles parallel to the compression direction. This texture is typical of materials with spinel structure deformed via the $\{$111$\}$$<$10-1$>$ and $\{$110$\}$$<$-110$>$ slip systems.
DE: 8162 Rheology--mantle
DE: 5120 Plasticity, diffusion, and creep
DE: 3902 Creep and deformation
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting