Petrology, geochemistry, and zircon U-Pb geochronology of the Zambezi Belt in Zimbabwe: Implications for terrane assembly in southern Africa

The Zambezi Belt in southern Africa has been regarded as a part of the 570-530 Ma Kuunga Orogen formed by a series of collision of Archean cratons and Proterozoic orogenic belts. Here, we report new petrological, geochemical, and zircon U-Pb geochronological data of various metamorphic rocks (felsic to mafic orthogneiss, pelitic schist, and felsic paragneiss) from the Zambezi Belt in northeastern Zimbabwe, and evaluate the timing and P-T conditions of the collisional event as well as protolith formation. Geochemical data of felsic orthogneiss indicate within-plate granite signature, whereas those of mafic orthogneiss suggest MORB, ocean-island, or within-plate affinities. Metamorphic P-T estimates for orthogneisses indicate significant P-T variation within the study area (700-780℃/6.7-7.2 kbar to 800-875℃/10-11 kbar) suggesting that the Zambezi Belt might correspond to a suture zone with several discrete crustal blocks. Zircon cores from felsic orthogneisses yielded two magmatic ages:2655±21 Ma and 813±5 Ma, which suggests Neoarchean and Early Neoproterozoic crustal growth related to within-plate magmatism. Detrital zircons from metasediments display various ages from Neoarchean to Neoproterozoic (ca. 2700-750 Ma). The Neoarchean (ca. 2700-2630 Ma) and Paleoproterozoic (ca. 2200-1700 Ma) zircons could have been derived from the adjacent Kalahari Craton and the Magondi Belt in Zimbabwe, respectively. The Choma-Kalomo Block and the Lufilian Belt in Zambia might be proximal sources of the Meso-to Neoproterozoic (ca. 1500-950 Ma) and early Neoproterozoic (ca. 900-750 Ma) detrital zircons, respectively. Such detrital zircons from adjacent terranes possibly deposited during late Neoproterozoic (744-670 Ma), and subsequently underwent high-grade metamorphism at 557-555 Ma possibly related to the collision of the Congo and Kalahari Cratons during the latest Neoproterozoic to Cambrian. In contrast, 670-627 Ma metamorphic ages obtained from metasediments are slightly older than previous reports, but consistent with ~680-650 Ma metamorphic ages reported from different parts of the Kuunga Orogen, suggesting Cryogenian thermal events before the final collision.