HR: 0800h
AN: U41B-0416    [Abstracts]
TI: Numerical simulations of mantle convection with a basal stagnant layer bearing high internal heating: implications on Earth's thermal and magnetic evolution
AU: * Costin, S O
EM: simona.costin@usask.ca
AF: University of Saskatchewan, Department of Geological Sciences 114 Science Place, Saskatoon, SK S7N 5E2, Canada
AU: Butler, S L
AF: University of Saskatchewan, Department of Geological Sciences 114 Science Place, Saskatoon, SK S7N 5E2, Canada
AB: In this contribution we present the results of numerical simulations of the thermal evolution of the Earth assuming a 200-km layer with high internal heating at the top of the core. Our models are inspired from recent isotopic studies that suggest the presence of a region with high internal heating residing in D^{' '} as an early enriched reservoir in incompatible elements (Boyet and Carlson, 2005, Tolstikhin and Hofmann, 2005). In addition, a chemically dense, distinct layer may be present in the lowermost mantle due to deep subduction (Hansen and Yuen, 1988) or possible iron enrichment (e.g. Tateno et al., 2007). The models consist of a spherical 2D axi-symmetrical model for convection in the mantle, underlain by a theoretical layer in which the heat is transferred through conduction (Lassiter, 2006). The numerical model of the mantle is coupled to a parameterized model for the thermal evolution of the core. The effects on the magnetic history and the age of the inner core are analyzed using the energy and entropy balances in the core. We compare our results with a previous study in which a high internal heating layer at the base of the mantle was allowed to participate in the whole mantle convection (Costin and Butler, 2006). We find that the presence of the stagnant layer reduces the amount of heat flow from the core and increases the age of the inner core. For models bearing more than 2 TW internal heating the heat flow from the core cannot sustain a magnetic field at early times. Our preferred model is represented by an enriched layer bearing no more than 0.5 TW radiogenic heating, for which the magnetic field exists throughout the entire evolution and predicts an inner core about 2.6 Ga old. In addition, we consider a mixed scenario in which the basal layer may be entrained in the whole mantle convection after 2.5 Ga of evolution (Davaille, 2007). For this case, the magnetic field is present over the entire geological time and the predicted age of the inner core is around 1.5 Ga.
DE: 1025 Composition of the mantle
DE: 1038 Mantle processes (3621)
DE: 1213 Earth's interior: dynamics (1507, 7207, 7208, 8115, 8120)
DE: 1507 Core processes (1213, 8115)
DE: 8125 Evolution of the Earth (0325)
SC: Union [U]
MN: 2007 Fall Meeting