HR: 1340h
AN: MR13B-1259    [Abstracts]
TI: Diffusivity of Diopside Liquid at High Pressure
AU: * Sun, N
EM: nsun@umich.edu
AF: University of Michigan, Department of Geological Sciences, 1100 N. University Ave, Ann Arbor, MI 48109, United States
AU: Stixrude, L
EM: stixrude@umich.edu
AF: University of Michigan, Department of Geological Sciences, 1100 N. University Ave, Ann Arbor, MI 48109, United States
AU: Karki, B B
EM: karki@bit.csc.lsu.edu
AF: Louisiana State University, Department of Computer Science, 283 Coates Hall, Baton Rouge, LA 70803, United States
AB: With the evidence of deep xenoliths and the seismic observation of ultra lower velocity zone (ULVZ), silicate liquids are thought to extend to the lower mantle and even to the core-mantle boundary. Knowledge of their physical properties at high pressures is essential to understand deep magma oceans. Diffusivity controls rates of chemical exchange, and is connected with the mobility (viscosity) of melts, and their response to elastic waves. In this study, we investigated the diffusivity of diopside liquid across the entire mantle pressure-temperature regime by first principles molecular dynamics (FPMD) simulations, which have been successfully used to study structure, equation of state, and thermodynamic properties of silicate liquids. Our simulations are based on density functional theory (DFT) in the local density approximation (LDA) and the ultra-soft plane-wave pseudopotential method. The calculations were performed with the Vienna ab initio simulation package (VASP). All simulations in this study were performed for an 80-atom cubic unit cell. For each calculation, the total run is 8 ps. Larger systems (160 atoms) were also performed and produced results within the statistical uncertainty of our simulations. We extract the self-diffusion coefficients via the mean-squared displacement and the Einstein relation. The calculated total diffusion coefficients are fit to the Arrhenius relation, D = D0 exp[-(E*+PV*)/kT]. This relation, with constant activation energy and volume does not capture all relevant behavior as a maximum diffusivity is observed at relatively lower pressure. Differences in the self-diffusion coefficients of different atoms are subtle.
DE: 3900 MINERAL PHYSICS
DE: 3924 High-pressure behavior
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting