Geomorphology of the Makgadikgadi Basin (Botswana): Insight Into the Propagation of the East African Rift System

Abstract

The Southwestern Branch of the East African Rift System propagates through the Central and Southern African plateaus and ends in the Okavango Makgadikgadi Zambezi Basin. This basin hosts the Okavango Graben and the Eiseb Graben, considered as the terminus of the Southwestern Branch of the rift. To the southeast, the Makgadikgadi Basin is affected by a series of normal faults forming the Makgadikgadi Rift Zone (MRZ) which regional geodynamic significance remains unclear. Based on fieldwork and geomorphic analysis, we revisited the geomorphological features associated with paleolakes and the fault pattern within the Makgadikgadi Basin to better constrain the dynamics of the MRZ. Fault scarps and offsets along linear dunes show normal‐dip kinematics of faults, indicating a NW‐SE extension direction in the area. Furthermore, lacustrine shorelines in the basin are undeformed, proving that they post‐date the fault activity. The previously published ages of these shorelines demonstrate that the MRZ currently has a low tectonic activity. Integrated in the geodynamic framework of the region, these results suggest that present‐day deformation shifts toward the Okavango Graben north of the MRZ. We therefore propose a “zip‐opening” model to explain the propagation of the Southwestern Branch of the East African Rift System where the tip of the system progressively progresses southwestward, driven by motions of the continental plates.