The Variable Seismic Signatures of Upwellings in the Transition Zone and Mid-mantle beneath Africa


More information here

The African superplume, is widely considered to have caused the ∼30Ma volcanism at the Ethiopian traps and has frequently been linked to other distinct loci of cenozoic volcanism across Africa. The contribution of more localised upwellings to African volcanism, that may or may not originate below the mantle transition zone is the subject of considerable debate. Observations of seismic discontinuities from the mantle transition zone and deeper within the mid-mantle can provide insight into the variable thermochemical nature of upwellings beneath Africa, that can be reconciled with their surface expressions. Here we present observations of seismic discontinuities beneath Africa obtained from a compilation of P-to-s receiver functions derived from publicly available seismograph networks across Africa from 1990 to the present day. We capitalise on a new high-resolution P-wave absolute velocity model for the African continent (Boyce et al., in prep.) to migrate our receiver functions to depth prior to common conversion point stacking. Our results illuminate a heterogeneous mantle transition zone beneath the East African and Main Ethiopian rifts. Preliminary results also indicate a seismic conversion from ∼1000km depth beneath the East African rift, co-located with slow wavespeeds associated with the African superplume, suggesting the presence of a mid-mantle phase transition within the plume material. These observations support the view that more than one mantle upwelling of variable thermochemical nature has contributed to recent volcanism in east Africa. Poster available here