HR: 09:00h
AN: MR21A-05 INVITED     [Abstracts]
TI: Dynamical Consequences of the Post-Perovksite Phase Transition and Implications for Radiative Heat Transfer in Deep Mantle.
AU: * Yuen, D A
EM: davey@msi.umn.edu
AF: Univ. of Minnesota, Dept. of Geology and Geophysics and Minnesota Supercomputing Institute, Minneapolis, MN 55455-0219 United States
AU: Matyska, C
EM: cm@karel.troja.mff.cuni.cz
AF: Charles University, Dept. of Geophysics. Faculty of Physics, Prague, 18000 Czech Republic
AB: The recent discovery of a phase transition from the perovskite ( PV) to post-perovskite ( PPV ) in the deep lower mantle has important implications for plume dynamics and physical properties in the lower mantle. The proximity of this exothermic phase transition to the core-mantle boundary would exert a profound influence on the generation of lower mantle plumes. We have employed a two-dimensional Cartesian model within the framework of the extended Boussinesq approximation for handling phase transitions for both the spinel to perovskite and the PV to PPV transition. An aspect-ratio 10 box is employed for variable viscosity. For the backgorund state we have used a depth-dependent thermal expansivity and a depth-dependent viscosity with a high viscosity peak in the lower mantle . Both constant and temperature-dependent viscosity models have been considered. The important distinction we found here is the thermal conductivity model. For a constant thermal conductivity model we obtained many small-scale instabilities and the lack of mega plume-like structures. This result does not depend on the type of viscosity employed. However, coherent large upwellings are obtained with the introduction of a temperature-dependent power-law radiative thermal conductivity ( Matyska et al., 1994). Cold downwellings have great difficulties reaching the base of the mantle because of efficient thermal assimilation by radiative transfer. Our findings point to the potential importance of radiative transfer in the deep mantle suggested recently ( Badro et al., 2004 ) , if one were to reconcile with both the existence of the PPV transition and the presence of the two mega slow velocity structures in the lower mantle, inferred from seismic tomography. Matyska, C., Moser, J. and D.A. Yuen, The potential influence of radiative heat transfer on the formation of megaplumes in the lower mantle, Earth Planetary Sci Lett., 125, 255-266, 1994. Badro, J., Rueff, J-P., Vanko, G., Monaco, G., Fiquet, G., and F. Guyot, Electronic transitions in perovskite: possible nonconvecting layers in the lower mantle, Science, 305, 383-386, 2004.
DE: 3900 MINERAL PHYSICS
DE: 3230 Numerical solutions
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting