Pleistocene to Recent rejuvenation of the Hebron Fault, SW Namibia

Abstract

Abstract The Hebron Fault in SW Namibia is associated with a <1 m to 9.6 m high scarp displacing Proterozoic basement and Middle to Late Pliocene crystalline conglomerates. The young age of strata exposed in the fault scarp together with evidence for displacement of aeolian dunes, post-dating the Middle Stone Age, suggests that latest fault displacements occurred during the Late Pleistocene to recent. Recorded historical seismic events show that the fault zone is still active. Latest movements of the fault are recorded by: down-to-the-SW offset of calcrete-cemented conglomerate; fluvially modified, asymmetric hanging wall, graben-like structures; at least two left-stepping jogs in the fault trace and structural data from basement rocks in which late-stage crush zones overprint earlier cataclasite. These features provide consistent evidence that the present scarp formed predominantly by normal dip-slip displacement on a NW-striking, steeply SW-dipping master fault with only a minor dextral strike-slip component. Strongly veined cataclastic fault rocks adjacent to the scarp in basement most probably originated at depths of 4–10 km. The conclusion is therefore that recent fault activity has reactivated a pre-existing, much older fault. Aerial photographic lineaments and similar fault scarps identified NW and SE of the present study area are interpreted as extensions of the same fault structure. Hence the total length of the Hebron Fault is at least 300 km subparallel to the Atlantic margin of southern Africa. Our observations confirm that the Hebron Fault is a neotectonic feature of regional significance that may relate to late Cenozoic and particularly Quaternary neotectonic activity in NE Namibia and NW Botswana.