Migmatites outcropping along the Omaruru River in the central Damara Orogen of Namibia are the product of both the injection of granitic material and in-situ partial melting of mainly pelitic greywackes. This partial melting event is mainly due to heat transfer from intruding granites during orogenic decompression at high temperatures. Anatexis under vapour-absent conditions in the deeper crust leads to dehydration melting of biotite in pelites and, to a lesser extent, in metagreywackes generating peraluminous garnet- and cordierite-bearing S-type granites which subsequently evolved through a complex assimilation and fractional crystallisation history (AFC). Anatexis under vapour-present conditions leads to the formation of in-situ leucosomes which are formed by disequilibrium melting of pelitic greywackes at T=690-710°C, P=4.6-5.5 kbar, XH2O=0.9 and ƒ02 between the QFM and NNO buffers. Disequilibrium melting is the favoured process for generation of the in-situ leucosomes and is probably related to an overstep of the wet solidus during infiltration of an aqueous fluid liberated from the crystallizing granites. The occurrence of contemporaneous hornblende-bearing granites with A-type affinities is probably linked with exhumation and uplift late in the tectono-metamorphic history.