The role of Edge-Driven Convection in the generation of volcanism-part 2: Interactions between Edge-Driven Convection and thermal plumes, application to the Eastern Atlantic

. In the eastern Atlantic Ocean, several volcanic archipelagos are located close to the margin of the African continent. This configuration has inspired previous studies to suggest an important role of edge-driven convection (EDC) in the generation of intraplate magmatism. In a companion paper (Manjón-Cabeza Córdoba and Ballmer, 2021: The role of Edge-Driven Convection in the generation of intraplate volcanism - part 1: a 2D systematic study, doi:10.5194/se-12-613-2021), we showed that EDC alone is insufficient to sustain magmatism of the magnitude required to match the volume of these islands. How- 5 ever, we also found that EDC readily develops near a step of lithospheric thickness, such as the oceanic-continental transition (“edge”) along the western African cratonic margin. In this work, we carry out 3D numerical models of mantle flow and melting to explore the possible interactions between EDC and mantle plumes. We find that the stem of a plume that rises close to a lithospheric edge is significantly deflected ocean-ward ( i.e. , away from the edge). The pancake of ponding hot material at the base of the lithosphere is also deflected by the EDC convection cell (either away or towards the edge). The amount of 10 magmatism and plume deflection depends on the initial geometric configuration, i.e. , the distance of the plume from the edge. Plume buoyancy flux and temperature also control the amount of magmatism, and influence the style and extent of plume-EDC interaction. Finally, comparison of model predictions with observations reveals that the Canary plume may be significantly affected and deflected by EDC, accounting for widespread and coeval volcanic activity. Our work shows that many of the peculiar characteristics of eastern Atlantic volcanism are compatible with mantle-plume theory once the effects of EDC on 15 plume flow are considered.

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