Geology of the Kenya Rift: An Introduction

The structural setting and Cenozoic origins of the East African Rift System (EARS) and its southward propagation are described with an emphasis on the eastern branch – the Kenya Rift. The possible role of mantle plumes, lithospheric thinning, pre-rifting structures (basement cratons, mobile belts, earlier rifts, basement foliations), domes, active and passive rifting are outlined. The chapter also describes the major features of accommodation zones, border faults, half-grabens, axial rift faults, monoclines and the major characteristics of Kenya rift basins and their role as sediment traps through time. Volcanics are largely absent in the western branch of the EARS whereas Neogene sodic volcanics dominate in the eastern branch. Volcanic lithologies include alkali basalts, comendites, rhyolite, trachytes, trachyphonolites and phonolites that erupted as either flood lavas or from central volcanoes located at regular intervals along the Kenya Rift. The spatial and temporal distributions of past eruptions are described. The geological evolution of the rift is presented along with schematic 3D models of past lakes and their palaeogeographic setting.