HR: 11:20h
AN: S11G-05    [PDF]
TI: Effect of variable heat production on the thermal evolution of the mantle
AU: * Kellogg, L H
EM: kellogg@geology.ucdavis.edu
AF: University of California, Davis, Geology Department, 1 Shields Avenue, Davis, CA 95616 United States
AU: Ferrachat, S
EM: sylvaine.ferrachat@wanadoo.fr
AF: University of California, Davis, Geology Department, 1 Shields Avenue, Davis, CA 95616 United States
AU: Natarajan, C S
EM: nsconjeepuram@ucdavis.edu
AF: University of California, Davis, Geology Department, 1 Shields Avenue, Davis, CA 95616 United States
AB: The Earth currently loses heat at about 44 TW; this reflects both cooling and radioactive decay. From cosmochemical models, the bulk silicate earth budgets of uranium, thorium, and potassium are thought to produce about 20 TW. Thermal history models, which balance the rate of heat loss against the resulting temperatures in the mantle, yield a slightly higher value of about 30 TW. This heat production is distributed among the continental and oceanic crust, mantle, and core. The total heat production in the depleted mantle (the MORB source), plus the crust, may total between 9.6 and 17 TW, leaving a substantial amount of heat unaccounted for (at least 3 to 10.4 TW, assuming that the cosmochemical models correctly estimate the bulk silicate earth.) The most likely reservoir for the excess is either in the deep mantle or in the core. We investigate the several models for the distribution of the excess heat within the mantle, using numerical models of convection. Our goal is to assess the effects on Earth's thermal history of a mantle reservoir of excess heat production. Such a reservoir could be formed, for example, by incomplete differentiation of the crust and mantle, or by separation and isolation of recycled oceanic crust. We concentrated on models with a moderate amount of excess heat production in a lower layer, while remaining within the constraints required above. The excess heat must be low enough to prevent an excessive temperature increase across any internal boundary layers. In models with two strictly isolated layers and equivalent total heat production, the temperature-dependent viscosity adjusts to maintain an equivalent temperature drop across the layers, regardless of the thickness of the layers. The regulation of viscosity by temperature is consistent with the results of earlier parameterized models of two-layered convection by a number of researchers. Using a double-diffusive model of two-component convection to relax the mass transfer constraint across the interface, we observe substantial topography on the boundary. We will discuss the effect of fully dynamical layering on the thermal evolution.
DE: 8125 Evolution of the Earth
SC: Seismology [S]
MN: 2003 Fall Meeting