Abstract:
We model the effects of a dense boundary layer at the base
of the mantle on the
thermal structure of D'' and the dynamics of convection in the
lower mantle. Using a finite element model of convection in
2-D with a Rayleigh number of 10^7, we include both thermal
and compositional effects on the density, and investigate the
effect of increasing thermal diffusivity in the dense layer
to simulate enrichment in metals. A dense boundary layer
tends to stabilize upwellings and decreases the heat
flow across the lower boundary. Increasing the
thermal diffusivity increases the temperature of upwelling
plumes and also reduces their tendency to drift laterally.
Convection within the dense layer can
create short wavelength variations in temperature, whereas
above the dense layer,
temperature variations show much longer wavelength variations
(1500 - 2000 km) which reflects the spacing of upwellings and
downwellings.
Increasing the thermal diffusivity in the layer tends to
suppress the small scale convection.