Age and correlation of the Proterozoic Mafingi Group in Malawi

The low-grade Mafingi Group form a restricted sequence of Proterozoic arenaceous and pelitic metasedimentary rocks which locally lie unconformably on the Palaeoproterozoic Ubendian Domain basement gneisses in northern Malawi. Four samples were taken from different parts of the sequence, in order to obtain detrital zircons for U–Pb geochronology to constrain their maximum age of deposition, provenance and thereby to suggest correlations with other sequences in the wider SE African region. Three samples, including one from the Type Area (Mafingi Hills), and two from different tectonic slivers within the Ubendian gneisses, gave maximum deposition ages of around 1800 Ma. A third sample, also from a tectonic sliver gave a much younger maximum depositional age of ∼1500 Ma. Apart from this, all samples show similar zircon age spectra, with a major composite age-peak at ∼1900 ± 100 Ma from zircon detritus most probably derived from the local Ubendian Domain basement. Three samples show a very small Archaean age component probably derived from the Tanzania Craton which lies to the NE. The most NE sample of strongly recrystallised “Virauli Quartzite”, apparently interlayered with Ubendian gneisses of the Ufipa Subdomain, contained metamorphic zircon grains dated at ∼560 Ma, reflective of a Pan-African overprint within the local western margin of the wider East African Orogen. Significantly, no evidence of ∼1 Ga (Irumide) metamorphism was detected in any of the samples.