Late Mozambique Belt structures in western Kenya and their influence on the evolution of the Cenozoic Kenya Rift

Abstract

The N-S-trending Late Proterozoic Mozambique Belt in western Kenya is characterized by steep Edipping foliation, generated during orogen-parallel shearing in sinistral ductile shear zones (Barsaloian event, ∼580 Ma). During the final stages of orogenic evolution, two NW-trending brittle sinistral fault zones, crossing the present Elgeyo Escarpment, were active (Loldaikan event, 580-530 Ma). One of these fault zones generated well-developed pseudotachylytes that are described in detail. A later dextral reactivation of the two fault zones is related to the latest event (Kipsingian event, 530-470 Ma) of the Mozambique orogeny. Petrological, geophysical and geological data show that the Kenya Rift follows the trace of an important crustal boundary between the Archean Tanzania Craton and the Proterozoic Mozambique Belt. Miocene extensional reactivation of the steep E-dipping ‘Barsaloian’ foliations at the Elgeyo and Nguruman Escarpments led to the formation of asymmetric rift basins bounded by E-dipping normal faults along the western rift margin. The brittle fault zones at the Elgeyo Escarpment, trending obliquely to the basement foliation are responsible for segmentation of the Elgeyo border fault and the abrupt change in the orientation of the northern Kenya Rift.