Geology of the Archaean Nzimane Inlier, Zululand

The Nzimane Inlier comprises several outcrops of Archaean basement rocks in the Hlabisa District, northeastern KwaZuluNatal, providing a glimpse into the nature of the poorly exposed, southeasterly part of the Kaapvaal Craton. The oldest rocks are a approximately 500-m-thick "greenstone" sequence of quartzites, Fe-rich and aluminous schists, and BIFs (banded iron formation) termed the Wela Formation. They are interpreted as having been derived from predominantly sedimentary protoliths (arenites, semi-pelites, pelites, and iron formations), in contrast to the typical volcanic-dominated greenstone sequences found to the west and north. The Wela Formation was deformed and metamorphosed under amphibolite facies conditions, thus providing a link between the typical greenschist facies greenstone assemblages in northwest Natal and Mpumalanga and the Archaean granulites of the Empangeni Group to the south. In the southern part of the inlier, approximately 950 m of low-grade ferruginous mudstones, rhythmites, fine-grained sandstones, and iron formations are exposed. These are interpreted as belonging to the Ntombe Formation, Mozaan Group, Pongola Supergroup, thus constituting the most easterly outcrops of Pongola strata yet identified and extending the known extent of the Pongola basin. The Pongola strata were intruded by a granitoid suite (the Nzimane Granite) with three phases, ranging from the oldest tonalite, through porphyritic monzogranite to the youngest fine- to medium-grained granite. The phases appear to be genetically related in a medium-K, calc-alkaline fractionation sequence. A single zircon evaporation date of 2733+ or -3 Ma was obtained from the coarse-grained porphyritic phase. This is considered to date its emplacement. The Nzimane Granite is similar in age and composition to the post-Pongola granites of northern Natal, Swaziland, and the late granites of the Barberton area, Mpumalanga.