TECTONIC MODEL FOR THE EVOLUTION OF THE LIMPOPO BELT

Constraints on which any model for the tectonic evolution of the Limpopo Belt must be based include the following data: crustal thickening to at least 65 km between approximately 2700 and 2650 Ma ago was responsible for the formation of the granulite terrane exposed in the Limpopo Belt today. This crustal thickening probably resulted from the thrusting of the Kaapvaal Craton over the Zimbabwe Craton along the south dipping, Triangle-Tuli-Sabi Shear Zone. Other northward-verging thrusts related to this event occur in the Kaapvaal Craton south of the Limpopo Belt. In the Central and Southern Marginal Zones and the Kaapvaal Craton, this shortening is directed to the southwest while in the Northern Marginal Zone, it was directed to the north-northwest. Peak metamorphism was superimposed on the thickened crust and then nearly isothermal decompression of several kbars occurred throughout the belt. During this decompression, rocks moved upward and spread outward onto the adjacent cratons from the zone of thickened crust along several inward directed shear zones, creating a regional "pop up". High-grade rocks were thrust over low-grade rocks on the cratons, producing along the terrane boundary retrograde metamorphism in the Limpopo Belt and prograde metamorphism on the cratons.