HR: 0830h
AN: T41C-0230    [PDF]
TI: Effect of Water on the Rheological Behavior of Fe-rich Olivine
AU: * Zhao, Y
EM: zhaoyh@pku.edu.cn
AF: University of Minnesota, Department of Geology and Geophysics 310 Pillsbury Dr. SE, Minneapolis, MN 55455 United States
AU: * Zhao, Y
EM: zhaoyh@pku.edu.cn
AF: Peking University, Department of Geophysics, Beijing, 100871 China
AU: Zimmerman, M E
EM: zimme030@umn.edu
AF: University of Minnesota, Department of Geology and Geophysics 310 Pillsbury Dr. SE, Minneapolis, MN 55455 United States
AU: Kohlstedt, D L
EM: dlkohl@umn.edu
AF: University of Minnesota, Department of Geology and Geophysics 310 Pillsbury Dr. SE, Minneapolis, MN 55455 United States
AB: The influence of water content on the rheological properties of Fe-rich olivine was investigated in order to better understand the influence of hydrogen on the creep behavior of mantle rocks. Triaxial compressive creep experiments were performed on fine-grained samples of Fo$_{50}$ and Fo$_{50}$ + water. Samples were fabricated from a mixture of powders of San Carlos olivine, Fo$_{90}$, and synthetic fayalite, Fo$_{0}$. The resulting Fo$_{50}$ material was ground into powders of $<$10 $\mu$m, cold-pressed into a Ni capsule, and hot-pressed at 300 MPa and 1533 K for 2 to 12 h. Two drops of water were added for the Fo$_{50}$ + water sample, which was then hot-pressed using a telescoping can to prevent the water from escaping. The final grain size of the resultant sample was 24-36 $\mu$m for dry Fo$_{50}$ and 24-45 $\mu$m for the Fo$_{50}$ + water sample. Samples were then deformed in a gas-medium apparatus at a confining pressure of 300 MPa and temperatures between 1223 and 1473K. The samples were deformed both in the diffusional and dislocation creep regimes, characterized by stress exponents of $\sim$1 and $\sim$3.5, respectively. Samples of Fo$_{50}$ deformed at a water fugacity of $\sim$300 MPa creep at a rate $\sim$15 times faster than samples of Fo$_{50}$ deformed under anhydrous conditions. This enhancement in strain rate is a factor of 2-3 greater than the enhancement in rate for Fo$_{90}$ aggregates deformed under similar conditions. The greater reduction in the viscosity of Fo$_{50}$ than in the viscosity of Fo$_{90}$, in going from anhydrous to hydrous conditions, is consistent with the observation that hydrogen solubility (and thus the degree of water weakening) increases with increasing iron content in olivine. Hence, rocks with increased iron content such as those believed to constitute the mantle of Mars may be considerably weaker under hydrous conditions than their counterparts within the mantle of Earth.
DE: 3902 Creep and deformation
DE: 5104 Fracture and flow
DE: 5120 Plasticity, diffusion, and creep
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8162 Rheology--mantle
SC: Tectonophysics [T]
MN: 2003 Fall Meeting