U–Pb detrital zircon dates and source provenance analysis of Phanerozoic sequences of the Congo Basin, central Gondwana

Abstract

The Congo Basin (CB) is the largest sediment sink of central Gondwana, built on a mosaic of Precambrian crustal blocks amalgamated during the mid-Paleoproterozoic (Eburnian; 2.1–1.8Ga), late Mesoproterozoic (Kibaran; 1.4–1.0Ga), and late Neoproterozoic–early Cambrian (Pan African; 750–500Ma). Sporadic uplift, tilting and erosion of these Precambrian terrains form the source regions for the sedimentary sequences that fill the CB. We investigate the Phanerozoic successions in the field and along four historic deep boreholes drilled in the center of the basin, and date detrital zircons from the main stratigraphic groups to characterize their provenance ages and reconstruct the paleogeographic evolution of the CB during amalgamation and break-up of the Gondwana supercontinent. Sedimentological data show that the oldest, upper Neoproterozoic–lower Paleozoic Redbeds (the Inkisi, Aruwimi and Biano Groups) were derived from the north. Zircons from these sequences have two dominant age-populations of 1100–950Ma and 800–600Ma, likely sourced from Kibaran and Pan African terrains within the Oubanguides (e.g. the Central Saharan Belt) and parts of the North African Shield (e.g. Darfour). The overlying Carboniferous–Permian glacial and deglaciation sequences (the Lukuga Group) have similar peaks, as well as abundant zircons of 2.05–1.85Ga and a subordinate number dated at 1.42–1.37Ga. The latter are from Eburnian and Kibaran sources in east-central Africa, consistent with west-facing glacial paleo-valleys preserved along the eastern margin of the CB. The succeeding Triassic (the Haute–Lueki Group) and Jurassic–Cretaceous (the Kwango Group) fluvial and aeolian red sandstones were again derived from the north. Their range of zircon dates has two main peaks at 1000Ma and 600Ma, but also contain small younger grains of 290–240Ma and 200–190Ma. We interpret these younger zircons to be derived from volcanic dust that originated during late Paleozoic–Jurassic magmatism of the Choiyoi and Chon Aike Provinces flanking the Andean subduction margin of Gondwana. By contrast, the uppermost Cenozoic alluviums of the CB (the Kalahari Group) contain diamond concentrates and large zircon fragments dated at 3–2.5Ga, derived from the Kasai and Cuango Cratons, to the south, which host Cretaceous diamondiferous kimberlites.