Geochronological evidence for an extension of the Northern Lobe of the Bushveld Complex, Limpopo Province, South Africa

Abstract

We have conducted the first geochronological study of the ultramafic–mafic succession (the Waterberg Project) located in the Southern Marginal Zone of the Limpopo Belt north of the Northern Lobe of the Bushveld Complex using U/Pb dating on zircons extracted from both mineralized reefs as well as on detrital zircons of the Waterberg Group unconformably overlying the mafics. This contribution is the first in a series of publications describing the well-mineralized succession and will therefore give an overview of the local geology. U/Pb baddeleyite ages for the main mafic sill intruding the area supplement the data. The succession is extremely well mineralized and therefore of interest to the wider geological community.The intrusion ages for the Lobe are 2059±3 and 2053±5Ma and within error coeval with the intrusion ages of the Bushveld Complex. Detrital zircon age probability density distributions indicate a maximum age of deposition of c. 2045Ma for the Waterberg Group and show abundant peaks of Archean age. Paleoproterozoic zircons are interpreted to represent zircon from the detritus of the now eroded roof rocks of the lobe, while the Archean zircons are most likely sourced from the Limpopo Complex to the northeast. The major dolerite sill intruding the project area has been confirmed to belong the Umkondo Igneous Province with a baddeleyite age of 1125±5Ma.The combination of these new age dates, local geology and existing literature is used to argue that (i) the ultramafic–mafic succession is related to the Bushveld Complex; (ii) a significant unconformity is present between igneous rocks and the overlying sediments, and (iii) the area was exposed to a level of Paleoproterozoic tectonism not previously observed in the Bushveld Complex.