The geochronology of the Limpopo Complex: A controversy solved

The results of 50 years of geochronological work in the Limpopo Complex are reviewed. The data defi ne three main age clusters. The oldest, at ca. 3.3 Ga, exists in the Central and Southern Marginal Zones and is defi ned by magmatic zircon dates. The second, with a genuine spread between 2.7 and 2.55 Ga, occurs in all three zones. It was a period of high-grade regional metamorphism with intense deformation and widespread anatexis, dated also mainly (but not exclusively) by zircon U-Pb. The third cluster is well constrained at 2.02±0.02 Ga in the Central Zone by zircon overgrowths, sparse magmatic zircons, monazite, apatite, Sm-Nd and Lu-Hf garnet dating, Pb/Pb discrete phase and stepwise leaching dating of garnet and titanite, and hornblende Ar/Ar dating. The Paleoproterozoic dates from metamorphic minerals are particularly associated with zones of intense transcurrent shearing at high-grade metamorphism. In the Northern Marginal Zone this event is more protracted, from 2.08 to 1.94 Ga, and defi ned in medium- to low-grade shear zones. In the Southern Marginal Zone it is absent. The evidence for both Neoarchean and Paleoproterozoic mineral ages, both defi ning high-grade tectono-metamorphic events, is in part paradoxical and has led to controversies as to the age of a proposed collisional orogeny. Studying the mineral dates in their tectonic context leads to the conclusion that fl uid access in deformation, rather than mere reheating, mainly caused their partial resetting in the Paleoproterozoic event. This allows the controversy to be resolved.