HR: 0800h
AN: U41B-0422    [Abstracts]
TI: How can the double crossings of the Post-Perovskite transition constrain the heat-flux from the core ?
AU: Monnereau, M
EM: marc.monnereau@orange.fr
AF: Observatoire Midi-Pyrenees, Laboratoire de Dynam. Terre et Planet., Toulouse, 31400, France
AU: * Yuen, D A
EM: daveyuen@gmail.com
AF: University of Minnesota, Minnesota Supercomputing Institute, Minneapolis, MN 55455, United States
AB: There are now accumulating seismic and mineral physical evidences supporting the dominating phase-change nature of the D" region. Therefore any local information on D" topography may provide a global constraint on the thermal boundary layer at the core- mantle boundary( CMB). For instance, it has been proposed that some pairs of discontinuities above the CMB deduced from seismic imaging may result in a double-crossing of the perovskite/post-perovskite phase transition by the geotherm at two different depths. Double-crossings may occur only when the CMB temperature, T-cmb is higher than the temperature of the phase transition at the pressure of the CMB. Thus, the confirmation of this observation would fix a lower bound for T-cmb, completely independent from the one provided by the melting curve of iron. There exists also the opportunity to put bounds on the thermal boundary layer thickness and then of the core heat flux with double-crossing.Using synthetic D" layer simulated by 3D spherical mantle convection, we show that double-crossing data can be explained by various models. We show that there exists a quantitative relationship between the fraction of basal heating used in the model( the ordinate ) and the Clapeyron slope ( the abscissa ) used to simulate the D" layer that fits the double-crossing data. The relationship follows a power-law dependence, y =x**beta, where beta is around - 0.3. This dependence is not sensitive to T- cmb in the range of 3500K to 4000K. However, this power-law relationship is more sensitive to the value of the thermal conductivity at the base of the mantle. Thus it appears possible to measure the core heat flow by the Clapeyron slope of the perovskite/post-perovskite phase transition. Lastly, we demonstrate from many simulations that, if the T-cmb does not exceed the temperature of the phase change at the pressure of the CMB by more than 200K, then we can fit the double-crossing data.
DE: 5430 Interiors (8147)
SC: Union [U]
MN: 2007 Fall Meeting