HR: 0830h
AN: S21E-0373    [PDF]
TI: Exploring the effect of variable material properties at depth on deep mantle convection
AU: * Naliboff, J B
EM: jbnaliboff@ucdavis.edu
AF: University of California, Davis, Geology Department, 1 Shields Avenue, Davis, CA 95616 United States
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: Turcotte, D L
EM: turcotte@geology.ucdavis.edu
AF: University of California, Davis, Geology Department, 1 Shields Avenue, Davis, CA 95616 United States
AB: Recent experiments on perovskite at high pressures suggest that conductive and radiative thermal transport prosesses may be substantially more efficient near the base of the mantle than near the surface (Badro et al., Science, v. 300, 789-791, 2003.) Experiments suggest that mantle viscosities will increase substantially in the lower mantle if the mantle has an adiabatic thermal gradient. Although the magnitude of these effects in the mantle remains to be established, a large increase in thermal conductivity and viscosity with depth could slow the rate of heat and mass transfer due to mantle convection and help maintain long-lived geochemical reservoirs in the lower mantle. In the extreme case, heat transport by convection might be negligibly small. However, the increase in viscosity will be somewhat offset by a reduction in viscosity due to increased temperature. We explore the possible effects of a substantial increase in thermal conductivity and viscosity on mantle flow, using finite-element models of mantle convection with strongly depth-dependent and temperature-dependent material properties. Tracer particles are included in the model to determine whether isolated reservoirs can be maintained in the lower mantle in this scenario. Since the magnitude of any viscosity and conductivity increase is not well-established in the mantle, we examine a wide range of possible material properties. A higher thermal gradient in the lower mantle can explain the large super-adiabatic gradient required for the whole mantle by core-mantle temperature constraints.
DE: 8125 Evolution of the Earth
SC: Seismology [S]
MN: 2003 Fall Meeting