Single zircon ages for granitoid gneisses in the Central Zone of the Limpopo Belt, Southern Africa and geodynamic significance

Ion microprobe, evaporation and vapour digestion single zircon emplacement ages for,granitoid rocks throughout the Central Zone (CZ) of the Limpopo mo bile belt, South Africa define three broad age groups, namely at 3188-3314, 2637-2734 and ca 2500 Ma, respectively. All these granitoids, including th e youngest group, display polydeformational features suggesting that much o f the tectonic history of the CZ occurred in the late Archaean and early Pr oterozoic. The oldest group of predominantly tonalitic-trondhjemitic-granodioritic gne isses was found in relatively small domains from the extreme W to the E of the CZ and probably represents remnants of a once more widespread early Arc haean terrain. The most abundant granitoid gneisses belong to the 2.6-2.7 G a age group and were emplaced into already ductilely deformed gneisses of t he oldest group. Several of these rocks were derived from intracrustal melt ing. Rare metamorphic zircons with ages of similar to 2560-2575 Ma reflect a high-grade metamorphic event in the CZ that has also been postulated by o ther workers. A strongly deformed orthogneiss with a protolith emplacement age of similar to 2510 Ma proves beyond doubt that at least part of the str uctural history in the CZ occurred in the early Proterozoic. An anatectic g ranite in the extreme W of the CZ intruded at similar to 2022 Ma and is pro bably related to the peak of granulite-facies metamorphism previously dated at 2027 +/- 6 Ma in the Messina area. The second period of granitoid magmatism is broadly contemporaneous with ch arnockite and enderbite emplacement and granulite-facies metamorphism in th e Northern and Southern Marginal Zones of the Limpopo belt. Broad contempor aneity of extensive granitoid magmatism in all three Zones raises doubts ab out the exotic nature of the CZ and suggests a revised evolutionary model f or the Limpopo belt. (C) 1999 Elsevier Science B.V. All rights reserved.