Mantle Wavespeed and Discontinuity Structure Below East Africa: Implications for Cenozoic Hotspot Tectonism and the Development of the Turkana Depression

Abstract Ethiopia's Cenozoic flood basalt magmatism, uplift, and rifting have been attributed to one or more mantle plumes. The Nubian plate, however, has drifted 500–1,000 km north since initial magmatism at ∼45 Ma, having developed above that now underlies the northern Tanzania craton low‐lying Turkana Depression. Unfortunately, our knowledge of wavespeed structure transition zone (MTZ) topography below these regions is poorest, due a historical lack seismograph stations. same data gap means we constraints on lithospheric in around NW–SE trending Mesozoic Anza rift. We exploit from new networks Depression neighboring Uganda develop AFRP22, African absolute P‐wavespeed tomographic model resolves whole along entire East rift system. also map MTZ thickness using Ps receiver functions. Africa's thinnest (∼25 thinning) northwest AFRP22 reveals co‐located, previously unrecognized, slow plume tail, extending MTZ, deep into lower mantle. This may thus contributed, with Superplume, development 45–30 Ma province preceded extension. Pervasive sub‐lithospheric wavespeeds imply Turkana's present‐day low elevation explained best by Cenozoic‐age crustal thinning. At ∼100 depth, illuminates fast SE Ethiopian plateau. In addition governing northernmost limit rifting, refractory nature this block likely minimized there.