The Response to Lufilian Folding of the Basement Complex around the Northern Edge of the Mpande Dome, Northern Rhodesia

Abstract

Work in parts of Northern Rhodesia has shown that some rocks formerly thought to be Katanga meta-sediments are schists and quartzites formed locally by shearing of basement gneisses and granite gneisses. On the northern margin of the Mpande dome, refoliation of the Basement Complex during the first intense deformation (Lufilian orogeny) of the Katanga System, and accompanying shearing, crushing, sericitization and silicification, has transformed granitic rocks into tectonites that are difficult to distinguish from overlying metasediments. Field and petrographic evidence of the deformation and reconstitution of the Basement Complex in seven localities on the northern margin of the dome and two on the western margin is detailed. The first stage in the transformation of granite gneiss into quartzite of tectonic origin is sericitization of feldspar and subsequent recrystallization and crushing; in many cases silicification accompanies sericitization and ultimately produces a rock indistinguishable from metasedimentary quartzite. Mica schist is another product of intense shearing. It is thought that migration of material during deformation leads to meta-morphic differentiation and the production of an alternation of quartzites and schists. Since the structures in the tectonites and metasediments are parallel, it is difficult and in places impossible to establish the position of the Katanga unconformity.