Gravity study of the structure of Suswa volcano and basement in the Kenya Rift

Abstract

The most remarkable gravity feature in the Kenya Rift Valley is a positive gravity lineation that accords with the spatial distribution of the microseismic, volcanic and geothermal activity. It is interpreted in terms of a hot mantle intrusion zone, 10–20 km wide, representing the heat source for many geothermal systems in the rift. Filtering and upward-continuation techniques have led to the identification of the gravity components associated with the complex caldera structure of Suswa volcano and sub-volcano formation, by modelling of the residual gravity data. Geophysical data indicate a model where ascending masses of material from the mantle are intimately coupled to the accumulation of a mafic melt at shallow depth in the area of Naivasha tectonic segment, where a geothermal field at Olkaria is under exploitation. High-frequency gravity data are consistent with volcanological and geophysical evidence in suggesting that the area of Late Quaternary caldera volcanoes, Olkaria, Suswa and Longonot, is a thermally privileged site.