A numerical study of thermal and chemical structures at the core-mantle boundary

Abstract

The core-mantle boundary (CMB) represents the lower boundary layer of the actively convecting Earth's mantle and is structurally very complex. Thermal and chemical structures such as thermal plumes and thermochemical piles have been considered to explain the complexities. Both affect the dynamics of the Earth's mantle and its temporal evolution. But also the surface plates are an essential aspect of mantle convection that strongly influence the dynamics of the interior.We use numerical thermochemical models of mantle convection to study the structure and dynamics of the lowermost mantle. Our approach allows for the investigation of plumes and piles in combination with plate-like surface motion and deep subduction. The models show that the presence of a dense CMB layer generally reduces the mobility of the surface plates but that during plate evolution a variety of plume classes occur leaving a complex structure at the CMB. The CMB topography shows large elevated areas with sharp edges and a flat or slightly dented top for piles with plumes atop. Also, plume clusters can cause large elevated areas with sharp edges but a flat top with a few smaller peaks. Smaller-scale patterns, often close to the edges of the large structures cause smaller peaks in CMB topography and can be explained by either line-plumes or wind-driven thermals. The latter often arise when heat is trapped beneath subducted slabs that spread over the CMB.