HR: 09:40h
AN: T41H-07 INVITED     [Abstracts]
TI: How do we Reconcile the Heat Budget of the Core with the Power Requirements for the Geodynamo?
AU: * Buffett, B A
EM: buffett@geosci.uchicago.edu
AF: University of Chicago, 5734 S. Ellis Avenue, Chicago, IL 60637 United States
AB: Regeneration of the magnetic field by convection in the core places demands on heat flow into the base of the mantle. If the heat flow is too low, thermal convection is shut off and the rate of generation of compositional buoyancy by solidification of the core becomes too low to sustain the geodynamo. Conversely, a large heat flow causes rapid growth of the inner core, so that convection prior to the appearance of the inner core must be sustained by thermal buoyancy alone. The attendant requirements on primordial heat become more severe as the age of the inner core decreases. Present-day estimates of temperature in the core suggest that the heat flow into the base of the mantle is 6 to 12 TW, which is sufficient to supply 1 to 2 TW of power to the geodynamo. However, when this range of heat flow is used in thermal history calculations we obtain a young inner-core age and an implausibly hot core temperature prior to 3 Ga. More reasonable thermal histories can be obtained using a lower heat flow if the power requirements for the geodynamo are substantially reduced (say 0.1 to 0.2 TW). On the other hand, a low heat flow appears to be incompatible with estimates of temperature in the core. There are two ways to reconcile the heat budget of the core with the power requirements for the geodynamo. First, we can add radiogenic heat sources to the core. These additional heat sources would slow the cooling of the core for a prescribed heat flow and extend the age of the inner core. Approximately 200 ppm of K in the core is sufficient to avoid unrealistic temperatures at early times. Alternatively, we can reduce heat loss from the core by accumulating radioactive isotopes into a layer that surrounds the core. Such a layer could form by segregating dense oceanic crust at the base of the mantle or by partitioning radioactive isotopes into a deep partial melt.
DE: 8115 Core processes (1507)
DE: 8125 Evolution of the Earth
DE: 8130 Heat generation and transport
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting