Two pulses of Mesoproterozoic intra-plate magmatism in the heart of the Palaeoproterozoic Ubendian Domain of northern Malawi

Abstract

Two Mesoproterozoic anorogenic igneous events are recorded in the Palaeoproterozoic Ubendian Domain in northern Malawi. The oldest is represented by the Mwakikome orthogneiss, a small peraluminous, sub-alkaline and ferroan syenogranite that has a U–Pb zircon emplacement age of 1411 ± 3 Ma, an initial εNd of ð€€€ 4.5 and a Nd TDM2 model age of 2.27 Ga. These data are interpreted to suggest that the Mwakikome intrusion was derived mainly from the melting of the adjacent Palaeoproterozoic country rocks during Kibaran-aged extension. The second anorogenic igneous event is defined by the more widespread Mwenga Suite, a series of small (<100 km2) NW-SE oriented and elongated plutons that occur in a narrow belt in the north of the Ubendian Domain. Seven samples from different intrusions gave U–Pb zircon emplacement ages between ~1150 and 1110 Ma. The Mwenga Suite is comprised of rocks that are also ferroan, potassic and sub-alkaline in composition and shows a range of major element compositions from monzogranite to alkali-feldspar granite. Nd isotopic data from one sample yielded an initial εNd of ð€€€ 2.2 and a Nd TDM2 model age of 1.88 Ga, suggesting that the suite was also largely derived from melting of the Ubendian host rocks, but with some additions from an enriched mantle source.