Mixing and the distribution of heterogeneities in a chaotically convecting mantle

Abstract

Chemical heterogeneities are introduced into the mantle by subduction of oceanic lithosphere and possibly by subduction of sediments and delamination of the continental lithosphere. These heterogeneities are blended into the mantle by convective mixing. Final homogenization is accomplished by diffusion. Numerical models of mantle convection suggest that it is chaotic. To study the effect of a chaotic flow on mixing, we have generated a space-filling, two-dimensional flow using the Lorenz equations in the chaotic regime as a driver. Mixing is very rapid; the mixing time for heterogeneities with an initial size of 6km is 240Ma for layered mantle convection; the corresponding mixing time for whole mantle convection is 960Ma. -from Authors