Quaternary volcanic centres of the Turkana Rift, Kenya

Abstract

Three small islands (North, Central and South Island) rise above the surface of Lake Turkana in northern Kenya. They represent the tops of Quaternary volcanic centres aligned along the axis of the Turkana Rift. They are links in the continuous chain of axial volcanic centres that run the length of the Eastern Branch of the East African Rift and represent the most recent additions to the architecture of the Rift. Mapping and petrographic studies reveal that the three island volcanic centres have many similarities in their general stratigraphy, structure, and geologic history; however, there are significant differences in relative lithologic abundances and compositions among them. The island volcanic centres are situated near the centres of each of a series of half-graben that are linked together along the length of the Turkana Rift. Estimates of the volumes of basaltic and intermediate volcanic components coupled with likely fractionation histories suggest that significant mafic-ultramafic intrusive complexes underlie the island volcanic centres. These are probably just the most recent additions to magmatically thickened, but mechanically thinned crust in this section of the East African Rift.