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U-Pb and Pb-Pb zircon ages for metamorphic rocks in the Kaoko Belt of northwestern Namibia: A palaeo-to Mesoproterozoic basement reworked during the Pan-African orogeny

Abstract:

The Kaoko Belt belongs to the Neoproterozoic mobile belt system of western Gondwana, whose geodynamic evolution is assumed to have resulted from collision between the Congo Craton (present Africa) and the Rio de la Plata Craton (present South America). Several magmatic intrusion periods can be distinguished in the coastal area of this belt, based on conventional U-Pb, SHRIMP and Pb-Pb evaporation analyses on zircons. The prevailing igneous rock types are of granitic to tonalitic composition. A Palaeoproterozoic terrain with U-Pb magmatic emplacement ages between -2.03 and 1.96 Ga may be correlated with the Eburnian event (-1.8 to 2.0 Ga), which is widespread in Africa. Additionally, two distinct magmatic events appear to be significant in the southwestern Congo Craton in late Palaeoproterozoic and Mesoproterozoic times, indicated by magmatic ages around 1.77 Ga and between -1.52 and -1.45 Ga. These two events have so far not been reported from the Dom Feliciano Belt (southeastern Brazil), which is considered to represent the South American counterpart of the Kaoko Belt. Therefore, a possible link of these two belts prior to the Pan-African orogeny (-750 to -450 Ma) can neither be confirmed nor rejected on the basis of our data. Emplacement ages for several Pan-African granitoids, obtained by U-Pb and SHRIMP analyses, range from -730 to -655 Ma. The youngest granitoids, representing the last major magmatic activity in that area, were emplaced at -550 Ma during a transpressional regime at peak Pan-African temperatures. © 2004 Geological Society of South Africa.