HR: 0800h
AN: U21A-0008    [Abstracts]
TI: Partially layered mantle convection and Earth's thermal history
AU: * Butler, S L
EM: sam.butler@usask.ca
AF: Department of Geological Sciences, University of Saskatchewan, 146 Science Place, Saskatoon, SK S7N 5E2, Canada
AB: Recent seismic tomographic images indicate that slabs penetrate through the 660-km depth phase boundary in some locations while they are deflected in their trajectory in others, suggesting that convection in Earth's mantle is currently partially layered at this depth. The efficiency of heat transport by convection decreases with increasing layering as heat must be carried by conduction across an internal thermal boundary layer. There is a long-standing problem concerning Earth's thermal history in that the heat flow at Earth's surface is significantly greater than what is thought to be the internal heat generation by radioactive decay. It has been suggested that layered convection may allow significant quantities of thermal energy to be stored in the lower mantle to be released later as the degree of mantle layering decreases over time which could allow for the observed high surface heat flow with relatively low internal heating. In this contribution, we simulate the thermal history of the Earth using a spherical axisymmetric numerical model of convection in Earth's mantle coupled with a parameterized model for the thermal evolution of the core. Layering is induced in the model by the effects of an endothermic phase transition at 660-km depth with varying magnitudes of the Clapeyron slope. We find that although the mean degree of layering increases with an increasing magnitude of the Clapeyron slope of the endothermic phase transition, the time-averaged thermal evolution is very similar to a whole-mantle model unless the magnitude of the Clapeyron slope of the phase transition is unreasonably large.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8125 Evolution of the Earth (0325)
DE: 8130 Heat generation and transport
SC: Union [U]
MN: 2007 Fall Meeting