Mantle transition zone structure beneath Tanzania, East Africa

We apply a three-dimensional stacking method to receiver functions from the Tanzania Broadband Seismic Experiment to determine relative variations in the thickness of the mantle transition zone beneath Tanzania. The transitio n zone under the Eastern rift is 30-40 km thinner than under areas of the T anzania:Craton in the interior of the East African Plateau unaffected by ri ft faulting. The region of transition zone thinning under the Eastern rift is several hundred kilometers wide and coincides with a 2-3% reduction in S wave velocities. The thinning of the transition zone, as well as the reduc tion in S wave velocities, can be attributed td a 200-300 degrees K increas e in temperature. This thermal, anomaly at >400 km depth beneath the Easter n rift cannot be easily explained by passive rifting and but is consistent with a plume origin for the Cenozoic rifting, volcanism and plateau uplift in East Africa.