The geology of the Natal Metamorphic Province in the Durban area

Abstract

This paper describes the field geology of the Natal Metamorphic Province (NMP) as exposed on the Durban 1:50 000 map sheet, and applies the established lithostratigraphic subdivision of the southern Mzumbe terrane to these rocks. Supracrustal gneisses of the Mapumulo Group are subdivisible into the constituent Ndonyane and Quha Formations. The Ndonyane Formation comprises a heterolithic sequence of quartzofeldspathic gneisses, whereas the Quha Formation is dominated by a variety of biotite gneisses and subordinate amphibolites. These rocks were intruded early in the evolution of the NMP by the distinctive I-type granitoids of the Mzumbe Suite and subjected to progressive deformation, in response to northeast to southwest directed compression. The A-type, late-syntectonic Oribi Gorge granitoids, represented in the field by both megacrystic and gneissic granites, were emplaced after the docking of the Margate and Mzumbe terranes and were subjected to only the waning stages of deformation. They were emplaced into and affected by large-scale transcurrent shear zones associated with the collision of the NMP and the Kaapvaal Craton to the north. In all, six NMP-related deformational events are recognised in the Precambrian rocks of the Durban area, and record the progression from ductile compression to ductile transtension and finally to pegmatite emplacement associated with brittle fracturing. The Durban area is characterized by steep planar fabrics and is a transcurrent-, rather than thrust-dominated sector of the NMP.