Geological and geophysical reconnaissance of the Lotikipi plain of northwestern Kenya and its relationship to the northern Kenya Rift

Abstract

The Lotikipi plain, located in the northwestern corner of Kenya, is a broad saucer-shaped depression surrounded by, and mainly filled by, volcanic rocks. Recently acquired geophysical surveys (gravity, magnetic, and seismic) show for the first time the structural configuration of this area and has resulted in an interpretation of its geological history within the framework of the evolution of the northern Kenya Rift. Two sub-basins have been recognized; the Lotikipi in the west and the Gatome in the east, separated by the Lokwanamoru range. They are dominantly filled by Oligo-Miocene volcanics, which are overlain by Late Tertiary(?) to Recent alluvial sedimentary deposits. The Lotikipi basin is characterized by relatively weak normal faulting and reaches a depth of approximately 4000 m. The Gatome basin is defined by a major down-to-the-east normal fault on its west margin and is approximately 6000 m deep. A thick sub-volcanic stratigraphic section, recognized from seismic data, suggests that the deepest part of the Gatome basin may be related to the Cretaceous Abu Gabra-Anza Graben rift trend. The commencement of volcanism in the Lotikipi plain during the Oligocene marked the earliest phase in the evolution of the northern Kenya Rift. This event preceeded the onset of significant extension of the upper crust and is interpreted as the result of a thermal anomaly in the mantle.