Evidence for Incipient Rifting in Southern Africa

Abstract

A study of microearthquakes in northern Botswana, September to December 1974 indicates that this region is tectonically active. Microearthquakes were found to occur primarily in a zone striking north-east from Lake Ngami through the Okavango delta to the Zambezi River. These events are associated with an en echelon set of north-easterly striking normal faults of Quaternary to Recent age, and appear to be continuous with the activity at Lake Kariba and continuing further north along the Luangwa valley to the main rift zone south-east of Lake Tanganyika. Focal mechanisms indicate normal faulting on NE striking planes. The tectonic setting of the Okavango delta thus appears to be that of a developing graben some 150 km wide. The delta is at the tip of a proposed incipient zone of rifting that follows an old post-Karroo, pre-Cretaceous rift zone. The African rifts are viewed as an incomplete, growing plate margin which is propagating to the south along at least two arms that bifurcate south of Lake Tanganyika.