HR: 09:00h
AN: U31A-03    [Abstracts]
TI: Impact of the Post-Perovskite Transition on the Structure of D
AU: van den Berg, A P
EM: berg@geo.uu.nl
AF: Dept. Theoretical Geophysics, Inst. Earth Sciences, Utrecht University, Budapestlaan 4, Utrecht, NL-3584 CD Netherlands
AU: * Yuen, D A
EM: davey@krissy.msi.umn.edu
AF: Department of Geology and Geophysics and Minnesota Supercomputing Institute, University of Minnesota, 117 Pleasant St. SE, Minneapolis, MN 55455-0219 United States
AU: Matyska, C
EM: cm@karel.troja.mff.cuni.cz
AF: Department of Geophysics, Charles University, V Holesovickach 2, Praha, 18000 Czech Republic
AB: The recently discovered phase transition of magnesium perovskite to a high pressure post-perovskite (PPV) structure has a direct impact on the complex constitution of the D" layer directly above the core mantle boundary. Strong lateral variations in seismic wave velocities in D" resulting in seismic wave diffraction, observed as PKIKP precursors (Cleary and Haddon,1972, van den Berg et al, 1978), could be connected with the PPV transition. Besides seismic wave velocity, thermal conductivity is also material dependent as shown in (Giesting et al., 2004) and (Badro et al., 2004). Phase dependent thermal conductivity therefore results in complex structures of thermo-physical parameters of the D" layer and a change in the style of mantle convection expressed in the propensity of plume generation from the CMB (Matyska and Yuen, 2004). We have investigated the impact of the new phase transition in mantle convection models including thermal coupling of the core. We apply an extended Boussinesq finite element model including latent heat production of the exothermic PPV phase transition. We apply a continuous representation of the dominant mineral phase in the description of the phase dependent thermo-physical parameters. The conductivity is adapted from the composite model of Hofmeister (1999), where we apply a phase dependent control parameter scaling the radiative conductivity component. Radiative thermal conductivity depends strongly on the temperature and in the post-perovskite phase even more so, because of the high-spin to low-spin transition as hypothesized by Badro et al. (2004). This way our model accomodates strong lateral variations of the phase boundary such that isolated patches of the high pressure phase show up above the CMB for a sufficiently high initial core temperature and high values of the Clapeyron slope, like the reported 7.5 MPa/K for the PPV transition (Tsuchiya, 2004). These patches are reflected in strong lateral variations of the phase dependent parameters which may explain the highly irregular character of the D" layer. The results also show strong space-time variations of the core/mantle heat flux of up to 100% of the background value. Such fluctuations would be expected to have a significant impact on geodynamo processes.
DE: 3924 High-pressure behavior
DE: 5134 Thermal properties
DE: 8121 Dynamics, convection currents and mantle plumes
SC: Union [U]
MN: 2005 Joint Assembly