Geology and geochronology of the Ubendian belt in Malawi; whither the Nyika Terrane

Abstract

The Palaeoproterozoic Ubendian Domain in Malawi comprises the SE segments of three distinct crustal blocks, namely (from north to south) the Mbozi, Ufipa and Nyika subdomains, apparently confirming the historic crustal subdivisions. Together, they represent about 30 % of the surface area of the entire Ubendian belt, most of which lies in Tanzania. We describe their geology and present 14 new U-Pb zircon dates of representative samples. The Mbozi Subdomain (SD) is predominantly comprised of mafic gneisses (Mbozi Group) with no Palaeoproterozoic granitoid intrusions. The Ufipa SD comprises several units of high grade supracrustal gneisses (Ufipa Group), with a maximum depositional age of ∼1990 Ma, deposited upon an interfoliated “cryptic” tonalite-granodiorite orthogneiss basement dated at ∼2150 Ma and occurring as scattered remnants within the paragneisses. Minor post-Ufipa Group granitoids were emplaced at 1990 Ma. The Nyika SD contains sequences of supracrustal gneiss (Nyika Group) deposited between ∼2100 and 1990 Ma, probably during at least two phases of sedimentation. There are numerous granitoids of varying compositions with an overlapping continuum of emplacement ages from ∼2045 to 1946 Ma, some of which are coeval with Nyika Group deposition. The youngest (post-tectonic) granites intrude the Nyika Group, but the status of the older foliated granitoids is less clear due to poor exposure.