Linear variation of major and trace elements in the Nk granite gneisses from the pluton can be explained by igneous fractionation involving plagioclase (10 wt.%), biotite (1 wt.%), alkali feldspar (13 wt.%) and LREE-enriched accessory minerals. The 87Sr/86Sr ratios become more radiogenic and δ18O values increase with increasing SiO2 indicating that in addition to crystal fractionation processes, the Nk granite gneisses were affected by assimilation processes involving contaminants similar to basement derived granites from the Central Damara orogen which show lower εNd (500 Ma) ratios. The protolith of the Nk granite gneisses is most likely a biotite- and/or amphibole-bearing but muscovite-free rock, most probably an intermediate igneous rock (i.e. diorite to granodiorite) or a metagreywacke. Concerning the isotopic differences between the granite gneisses from the pluton and the gneissic granitic veins, partial melting probably took place in a heterogeneous compositionally layered middle to lower crust at temperatures of 845 ± 10 °C as calculated by monazite and zircon saturation equations.
The final stages of continental collision during westward dipping subduction of the Kaoko belt beneath the Ribeira belt took place between ca. 590 and 520 Ma. In view of such a Pan-African subduction zone related geotectonic situation, the Nk granite gneisses are products of melting events in arc-derived rocks, produced in an earlier stage of the Pan-African orogeny.