African Cenozoic hotpot tectonism: new insights from continent-scale body-wave tomography


More information here

The African plate is an ideal study locale for mantle plumes and Cenozoic hotspot tectonism. On the eastern side of the continent, the uplifted East African and Ethiopian plateaus, and the 30Ma Ethiopian Traps, are widely considered to be the result of the African Superplume: a broad thermochemical anomaly that originates below southern Africa. Precisely where and how the superplume traverses the mantle transition zone is debated however. On the western side of the continent, the Cameroon Volcanic Line is a hotspot track with no age-progression; it is less easily attributed to the effects of a mantle plume. Central to our understanding of these issues is an improved picture of mantle seismic structure. Body-wave studies of African mantle wave-speed structure are typically limited to regional relative arrival-time studies that utilize data from temporary seismograph networks of aperture less than 1000km. The resulting tomographic images are higher resolution than continent-scale surface-wave models, but anomaly amplitudes cannot be compared from region to region using the relative arrival-time approach: the 0% contour in each region refers to the regional, not global mean. The challenge is thus to incorporate the often-noisy body-wave data from temporary seismograph networks into a continent-scale absolute delay-time model. We achieve this using the new Absolute Arrival-time Recovery Method (AARM) method of Boyce et. al., (2017) and the tomographic inversion approach described by Li et. al., (2008). We invert for mantle wavespeed structure using data recorded since 1990 by temporary networks in the Atlas Mountains, Cameroon, South Africa, East African Rift system, Ethiopia and Madagascar. Our model is well resolved to lower mantle depths beneath these temporary networks, and offers the most detailed picture yet of mantle wavespeed structure beneath Africa. The contrast between East African and Cameroon mantle structure suggests multiple development mechanisms for hotspot tectonism across the African continent.