The Connection Between Okavango (Botswana) and Kafue (Zambia) Rift Zone from Satellite Gravity and Aeromagnetic Data: Implication for the Evolution of the Southwestern Branch of the East African Rift System

Abstract

We analyzed gravity and magnetic data to investigate the lithospheric connection between the Okavango Rift Zone (ORZ) in northwestern Botswana and the Kafue Rift Zone (KRZ) in Zambia. The tectonic environment and the lithospheric structure of the ORZ is well understood, the lithospheric structure of the KRZ and surrounding region is basically unknown. Determining this lithospheric structure and how or if the ORZ and KRZ are tectonically related, a gravity and magnetic data analysis using a power spectrum analysis combined with the two-dimensional gravity forward models constrained by seismic data was conducted. The gravity power spectrum analysis indicated that the crust was thinned by between 4 and 5 km beneath both rift zones compared to the surrounding Proterozoic terranes, with the depth to the Mid Crustal Discontinuity (MCD) thinned by 2–3 km. Additionally, the gravity models suggested that the region between the ORZ and KRZ exhibits a shallower depths to the Moho and MCD, which implies that rifting process is an ongoing process that links these rift zones A derivative analysis of the aeromagnetic data analysis indicated that the fabric of the Proterozoic crystalline basement structures aligns parallel to the ORZ and the power spectrum analysis that showed that the depth to basement within the transfer zones between the basins were deeper, implying that the basins are tectonically linked. The basement fabric is perpendicular to the KRZ which implies that the ORZ was formed in a structurally weak zone between the Congo and Kalahari Cratons and that block rotation within the KRZ region facilitated the extension that formed the rift. Though there is age difference between the ORZ and KRZ, the connectivity of the two rift zones indicates that there is a continuation of the Western Branch of the East African Rift System from Zambia into Botswana.