Lowermost mantle flow at the eastern edge of the African Large Low Shear Velocity Province

Observations of seismic anisotropy in the lowermost mantle are plentiful, but their interpretation in terms of mantle flow remains challenging. Here we interrogate the anisotropic structure of the lowermost mantle beneath the Afar region, just outside the edge of the African Large Low Shear Velocity Province, using a combination of shear wave splitting techniques applied to phases propagating at five distinct raypath orientations. We then model the resulting data set by testing various candidate mechanisms for anisotropy. The observations are best fit by a model that invokes the lattice preferred orientation (LPO) of post-perovskite, with the [100] crystallographic axis oriented either nearly vertically or highly obliquely to the horizontal plane. Plausible corresponding mantle flow scenarios involve a significant vertical flow component, which suggests that the African Large Low Shear Velocity Province edge may deflect ambient mantle flow upwards or may be associated with a sheet-like upwelling.