Broadband seismic experiments probe the East African Rift

To further advance our understanding of how and why continents rift apart, the upper mantle structure beneath east Africa is being investigated by three Incorporated Research Institutes of Seismology/Program for the Array Seismic Studies of the Continental Lithosphere (IRIS/PASSCAL) broadband seismic experiments. The origin of Cenozoic rifting in east Africa, along with the volcanism and plateau uplift found there, has long fascinated Earth scientists. The rift system can be linked to extensional stresses associated with the development of the Afar triple junction, but it is unlikely that the small amount of crustal extension, ≤10–15 km, across east Africa could have led to sufficient pressure‐release melting to account for the large volume of extrusive rock present in some parts of the rift system, or enough thinning of the lithosphere to cause plateau uplift ≥1 km. Consequently, a purely “passive” origin for the Cenozoic extensional tectonism has been frequently rejected. Instead, it has been commonly attributed to one or more mantle plumes, a view supported strongly by geochemical evidence. However, non‐plume models cannot be ruled out completely, based on existing observations of mantle structure and composition, nor is it clear how many plumes might be present beneath east Africa.