HR: 09:45h
AN: U31A-06    [Abstracts]
TI: Initiation of Thermo-Chemical Plumes from the Post-Perovskite Layer
AU: * Connolly, J A
EM: james.connolly@erdw.ethz.ch
AF: Department of Earth Sciences, Swiss Federal Institute of Technology, Zurich, 8092 Switzerland
AU: Gerya, T
EM: taras.gerya@erdw.ethz.ch
AF: Department of Earth Sciences, Swiss Federal Institute of Technology, Zurich, 8092 Switzerland
AU: Yuen, D A
EM: davey@krissy.geo.umn.edu
AF: Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455 United States
AB: The recent discovery of a stability field for the post-perovskite phase in the deep mantle has strong consequences for the origin and petrology of lower-mantle plumes that develop in proximity of the core-mantle boundary. In order to study dynamics, geometry and mineralogical composition of such plumes we have implemented a self-consistent petrological-thermomechanical model of the lower mantle, wherein we have included density changes due to phase transitions involving post-perovskite in both the continuity and the momentum equations, and latent heat of mineral reactions and adiabatic and shear heating in the energy conservation equation. The model accounts for dependence of thermal conductivity, which has a strong radiative component, on temperature, pressure and composition (decreasing with increasing Fe-content). The petrological model covers the entire mantle and is derived by free energy minimization together with estimates for the thermodynamic properties of post-perovskite, perovskite, wuestite and various mid-mantle silicates. This approach precisely quantifies the thermodynamic and mechanical influence of the post-perovskite and perovskite forming phase transformations, which depend on temperature, pressure and composition .We have applied a well-tested marker-in-cell method and conservative finite-differences to solve governing equations in 2-D. During generation of thermal-chemical plumes temperature and mantle composition counteract introducing complexity in plume dynamics. We will test the various possibilities and conditions for mega- plume structures and investigate the stable and collapsing (oscillating) end-members that are expected to limit the range of behavior that may arise as result of lower mantle complexity. Also of interest is the fate of the descending down-wellings, as they will be heated up and softened by the post-perovskite transition.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
SC: Union [U]
MN: 2005 Joint Assembly