Seismic evidence for a deep upper mantle thermal anomaly beneath east Africa

Upper mantle seismic velocity variations beneath northern Tanzania coupled with the structure of the 410 and 660 km discontinuities reveal a 200-400-k m-wide thermal anomaly extending into but not necessarily through the trans ition zone beneath the eastern branch of the East African rift system. This finding is not easily explained by small-scale mantle convection induced b y passive stretching of the lithosphere or by a broad thermal upwelling ext ending from the lower mantle into the upper mantle, but it can be attribute d to a mantle plume, provided that a plume head is present under the lithos pheric keel of the Tanzania craton. A plume interpretation for the deep the rmal anomaly is supported by evidence for mantle having the geochemical cha racteristics of a plume at >150 km depth beneath northern Tanzania.