Metamorphic evolution and tectonic significance of Neoarchean high-pressure mafic granulites in the Central Limpopo Belt, South Africa.

The Sand River area is in the northeastern part of the Central Zone (CZ) of the Limpopo Belt, and represents a key terrane to reveal early Precambrian tectonic processes in southern Africa. Based on petrology, U–Pb zircon ages, and major and trace element data of high-pressure (HP) mafic granulites from the Sand River area, the tectonic evolution of the Central Zone of the Limpopo Belt is re-evaluated here that allows revision of previous interpretations. The protoliths of the HP mafic granulites and amphibolites are sub-alkaline tholeiitic basalts similar to those formed at a mid-ocean ridge and intruded at 2.8 Ga. Based on the distinct mineral assemblages, three metamorphic stages (M₁–M₃) are recognized in the studied samples: (1) a peak HP granulite facies stage M₁ (~1.17–1.32 GPa/~825–870°C), (2) a post-peak near-isothermal decompression stage M₂ (~0.70–0.73 GPa/~835–880°C), and (3) a later, independent metamorphic stage M₃ (~0.53–0.69 GPa/~793–801°C). M₁ and M₂ define together a clockwise P–T path. It reveals important information related to the Neoarchean collisional orogeny, and its later overprinted by an independent orogeny with subsequent exhumation and cooling. U–Pb zircon dating of two mafic granulites samples yielded protolith formation of the mafic granulites is prior to ~2.72 Ga, and the two metamorphic age peaks of ~2.72 (M₁) and ~2.0 Ga (M₃), which present the peak and post-peak cooling stages, respectively. The metamorphic evolution of HP mafic granulites in the Sand River area as reconstructed in this study suggests the Neoarchean collision of the Kaapvaal and Zimbabwe cratons and a discrete Paleoproterozoic orogenic overprint followed by post-orogenic exhumation and cooling. [ABSTRACT FROM AUTHOR]