A tomography study of the Chyulu Hills, Kenya

Abstract

The Chyulu Hills, a Quaternary volcanic field on the eastern shoulder of the Kenya rift in East Africa, have been the target of a multidisciplinary research project. In this contribution teleseismic travel-time residuals from a passive seismic experiment are imaged into P-velocity perturbations in the lithosphere underneath the Chyulu Hills. The images reveal lateral velocity contrasts of about 5% with a prominent low-velocity zone which is located directly beneath the volcanic range down to 70 km depth. Due to the small size and amplitude of the anomaly this zone of decreased seismic velocity is interpreted as evidence for small magma chambers with elevated temperatures in the lower crust and uppermost mantle. A major upwelling of the asthenosphere can be excluded, because the seismic anomaly is too limited in size. However, the increased temperatures below the Chyulu Hills are interpreted as a sign for the still active magmatic processes related to the rifting in East Africa.