The internal structure of the African superplume; insights from body-wave seismic tomography and converted phases


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Originating below southern Africa, the African superplume, is a ubiquitous observation in global seismic tomographic images as a broad thermochemical anomaly. It is widely considered to have caused the ~30Ma volcanism at the Ethiopian traps and uplifted plateaus of eastern Africa. However, exactly how and where this feature crosses the mantle transition zone is debated. Further, internal heterogeneity within the plume itself has not been unambiguously observed, features predicted following studies of the south Pacific superplume. Key to resolving these issues are detailed seismic tomographic images and localised short-wavelength observations from converted seismic phases. Continental-scale surface wave imaging is lower resolution than regional body-wave studies of the mantle beneath Africa. The often-noisy data derived from these temporary networks of <1500km aperture, is routinely processed using relative arrival-times but these datasets cannot be combined across the entire African plate due to the loss of the mean background velocity structure. The development of Absolute Arrival-time Recovery Method (AARM) method of Boyce et. al., (BSSA: 2017) allows incorporation of P-wave data from all networks that have operated since 1990 in the Atlas Mountains, Cameroon, South Africa, the East African Rift system, and Ethiopia into the most up-to-date continental absolute delay-time P-wave mantle tomographic model for the African continent. Our model is well resolved to lower mantle depths beneath these temporary networks. We also present a new compilation of receiver function stacks that help constrain topography of sharp discontinuities above the south African LLSVP within the superplume.