LATE MOZAMBIQUE BELT STRUCTURES IN WESTERN KENYA AND THEIR INFLUENCE ON THE EVOLUTION OF THE CENOZOIC KENYA RIFT

The N-S-trending Late Proterozoic Mozambique Belt in western Kenya is characterized by steep E-dipping foliation, generated during orogen-pa rallel shearing in sinistral ductile shear zones (Barsaloian event, ap proximately 580 Ma). During the final stages of orogenic evolution, tw o NW-trending brittle sinistral fault zones, crossing the present Elge yo Escarpment, were active (Loldaikan event, 580-530 Ma). One of these fault zones generated well-developed pseudotachylytes that are descri bed in detail. A later dextral reactivation of the two fault zones is related to the latest event (Kipsingian event, 530-470 Ma) of the Moza mbique orogeny. Petrological, geophysical and geological data show tha t the Kenya Rift follows the trace of an important crustal boundary be tween 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 th e western rift margin. The brittle fault zones at the Elgeyo Escarpmen t, trending obliquely to the basement foliation are responsible for se gmentation of the Elgeyo border fault and the abrupt change in the ori entation of the northern Kenya Rift.