The Limpopo metamorphic belt, South Africa: 1. Geological setting and relationship of the granulite complex with the Kaapvaal and Zimbabwe cratons

The Limpopo granulite belt of southern Africa is subdivided into a Central Zone, and a Southern and Northern Marginal Zones. The Central Zone is characterized by a unique shelf-type supracrustal succession intruded by a layered igneous complex, while the two marginal zones are typified by tectonically dismembered greenstone slivers, which are intimately mixed with migmatized tonalitic gneisses. The Central Zone is separated from the marginal zones by inward-dipping mylonitic shear zones with strike-slip characteristics, while the two marginal zones are separated from the adjacent granite-greenstone cratons by inward-dipping thrust zones. Geophysical, structural and metamorphic data all support a model that incorporates north-south-directed thrusting (D1) across the entire belt that resulted in the formation of the granulite terrain exposed in the LB today. During subsequent uplift and unroofing of the thickened crust, rocks moved upwards and outwards onto the adjacent granite-greenstone cratons along the inward directed shear zones (D2) that bound the two marginal zones. This created a regional pop-up. High-grade rocks uplifted and thrusted onto the low-grade rocks of the two adjacent cratons suffered decompression and subsequent retrograde metamorphism, while the under-thrusted low grade rocks underwent prograde metamorphism. The timing of thrusting in the marginal zones is constrained to a minimum age of about 2.627 Ga by the emplacement of syntectonic chamockitic granitoids that clearly intrude D2 shear zones.