Helium isotopes at Rungwe Volcanic Province, Tanzania, and the origin of East African Plateaux

We report helium isotope ratios (He-3/He-4) of lavas and tephra of the Rungwe Volcanic Province (RVP) in southern Tanzania. Values as high as 15R(A) (R-A = air He-3/He-4) far exceed typical upper mantle values, and are the first observation of plume-like ratios south of the Turkana Depression which separates the topographic highs of the Ethiopia and Kenya domes. The African Superplume - a tilted low-velocity seismic anomaly extending to the core-mantle boundary beneath southern Africa - is the likely source of these high He-3/He-4 ratios. High He-3/He-4 ratios at RVP together with similarly-high values along the Main Ethiopian Rift and in Afar provide compelling evidence that the African Superplume is a feature that extends through the 670-km seismic discontinuity and provides dynamic support - either as a single plume or via multiple upwellings - for the two main topographic features of the East Africa Rift System as well as heat and mass to drive continuing rift-related magmatism. Citation: Hilton, D. R., S. A. Halldorsson, P. H. Barry, T. P. Fischer, J. M. de Moor, C. J. Ramirez, F. Mangasini, and P. Scarsi (2011), Helium isotopes at Rungwe Volcanic Province, Tanzania, and the origin of East African Plateaux, Geophys. Res. Lett., 38, L21304, doi:10.1029/2011GL049589.