Seismic images illustrate the deep roots of the Chyulu Hills volcanic area, Kenya

Abstract

A recent delay time tomography experiment has revealed the still ongoing processes that formed the East African Rift, the world's largest continental rift system. These new data have been used to produce tomographic images of the crust and upper mantle beneath the Chyulu Range (Figure 1), a Quaternary volcanic field on the rift's eastern shoulder.

The images show a prominent low-velocity zone where the youngest volcanism occurred directly beneath the Chyulu Range. Velocity contrasts as large as 4% have been found in 40–90 km depth (Figure 1). The reduced seismic velocity beneath the volcanic range probably suggests the presence of small active magma chambers in the crust and upper mantle. A large-scale asthenospheric upwelling underneath the rift shoulder is excluded as cause of the volcanism because the anomaly is too small in size as well as in percentage of velocity reduction.