HR: 0800h
AN: GP41B-0874    [Abstracts]
TI: Anisotropic and Isotropic Effective Olivine Medium Models
AU: * Du Frane, W L
EM: wd@asu.edu
AF: Arizona State University, Department of Geological Sciences Box 871404, Tempe, AZ 85287-1404 United States
AU: Tyburczy, J A
EM: jim.tyburczy@asu.edu
AF: Arizona State University, Department of Geological Sciences Box 871404, Tempe, AZ 85287-1404 United States
AU: Roberts, J J
EM: roberts17@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Ave L-201 , Livermore, CA 94551 United States
AU: Toffelmier, D A
EM: dat@asu.edu
AF: Arizona State University, Department of Geological Sciences Box 871404, Tempe, AZ 85287-1404 United States
AB: New experimental techniques are used to accurately measure the electrical conductivity (σ) of single crystal San Carlos olivine (Fo_89.1) along each principal orientation. The temperature (1100, 1200, and 1300°C) and oxygen fugacity (10^-7<fO₂<10¹ Pa) conditions encompassed allowed us to model the separate dependences of σ on T and fO₂ with an undifferentiated mixed conduction model of small polarons and Mg vacancies to obtain steady-state fO₂-independent activation energies: Ea_[100] = 0.32 eV, Ea_[010] = 0.56 eV, Ea_[001] = 0.71 eV. A nonspecific fO₂-independent parameter, σ_min, is necessary to fit the data and absorbs the conductivity contributions of electrons and extrinsic defects. The model is of the form σ_Tot = σ₀fO₂e^-Ea/kT + σ_mine^-Ea/kT, and provides an effective olivine medium for each principle orientation, suitable for use over the upper mantle temperature range and a range of oxygen buffer assemblages. A [100]-lattice preferred oriented layer of dry olivine would provide a maximum of ~10^0.5 S/m azimuthal conductivity contrast for T = 1500°C. The anisotropic results are combined to create an isotropic model with steady-state fO₂-independent Ea = 0.53 eV. The inclusion of the σ_min results in conductivity that is ~0.6 log units higher than the previous SO1 and SO2 models for T = 1000°C. The difference between this model and the previous SO1 and SO2 models become larger with decreasing T. This work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under contract W-7405-ENG-48 and supported specifically by Laboratory Directed Research and Development funding.
DE: 1515 Geomagnetic induction
DE: 3904 Defects
DE: 3914 Electrical properties
DE: 5109 Magnetic and electrical properties (0925)
DE: 8162 Rheology: mantle (8033)
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005