KAFUE RIFT: THE FORGOTTEN SEGMENT OF THE SOUTHWESTERN BRANCH OF THE EAST AFRICAN RIFT

We examined the surface and near-surface structures of the Kafue rift in south-central Zambia using Shuttle Radar Topography Mission (SRTM) Digital Elevation Models (DEM) and high-resolution aeromagnetic data. Little is known about this structure except that it might be a Mesozoic extension of the Southwestern Branch of the East African Rift system (EARS). The Kafue rift is located to the northwest of the Mid-Zambezi rift and to the northeast of the Okavango Rift Zone, which is suggested as the youngest and most southern expression of the Southwestern Branch EARS. The Kafue is underlain by the Precambrian-Paleozoic Lifilian Arc at the northwestern edge of the Mesoproterozoic-Neoproterozoic Irumite Belt This work entailed first using different hill shading techniques to improve the SRTM DEM to examine brittle structures in the region. Second in order to understanding the three dimensional (3D) surface and near-surface structure we extracted NW-SE and N-S topography profiles. These were interpreted to create idealized geologic cross-sections. Third, to map the underlying Precambrian structure we used the horizontal and vertical derivatives and negative and positive tilt of the total magnetic intensity of aeromagnetic data. Our work found the following: 1) the Kafue forms a left stepping feature with the Okavango Rift Zone in the southwest, while in the northeast the Kafue bends eastwards towards the Mid-Zambezi rift. 2) Overall the Kafue appears to be a south dipping half-graben with a north-northwestern border fault, and the southeastern portion of the Kafue appears to be a flexure zone. 3) The Kafue itself is characterized by broad long-wavelength magnetic anomalies suggestive of the presence of rift sediments fill, while boarding regions contain short-wavelength magnetic anomalies, reflective of the Precambrian ductile structures, such as those dominating the Mwembeshi Shear Zone. We suggest that the Kafue forms a complex extensional pathway linking the Okavango Rift Zone with the Mid-Zambezi Rift. It’s also possible that the Precambrian structures are exhibiting first order [thin lithosphere associated with orogenic belts] and second order [presence of discrete shear zone] in localizing extensional strain during the onset of the Kafue rift.