Thermochemical structure and dynamics of the African superplume

[1] We present a new three-dimensional (3-D) model of the thermochemical structure of the African superplume region obtained from simultaneous inversion of global seismic and convection-related data. Convection-related observations include the global free-air gravity field, tectonic plate motions, dynamic surface topography and the excess ellipticity of the core-mantle boundary. A 3-D image of the chemically-induced density perturbations provides direct evidence that intrinsically-dense material is entrained within the superplume and concentrated into a rounded structure similar to 1000 km above the core-mantle boundary. The thermally-induced density perturbations are greater in magnitude than the chemically-induced implying overall positive buoyancy throughout the superplume. The observed morphology and density signatures are consistent with a thermochemical plume that has risen from a compositionally-distinct 'pile' at the base of the mantle and may be currently deforming under the influence of its intrinsic negative chemical buoyancy.