Crustal Evolution of the Northern Nyika Subdomain of the Palaeoproterozoic Ubendian Belt in Malawi

The Ubendian belt extends from eastern Congo through SW Tanzania and NW Zambia across northern Malawi and into Mozambique. It results from the Palaeoproterozoic accretion of a number of crustal blocks followed by the collision of the Tanzanian and Congo cratons. The Ubendian belt has been classically divided into eight "terranes", (termed "subdomains" in this work), based on rock assemblage, magmatic and metamorphic history. This paper is concerned with the geological evolution of the southernmost of these, the Nyika Subdomain. We present an extensive dataset to decipher the geological history of the northern part of the Nyika Subdomain, including field observation, LA-ICP-MS U/Pb geochronology on zircon and monazite and a metamorphic petrological study of the extensive characteristic migmatitic cordierite-bearing gneisses. The U/Pb zircon data records four magmatic pulses. The first is represented by xenocrysts dated between 2200 and 2150 Ma. The second, major pulse is dated at ca. 2030 Ma, followed by minor magmatic activity at ca. 1980 Ma. This event is coeval with regional granulite facies metamorphism (ca. 780 degrees C and 0.6 Gpa), constrained in age U/Pb monazite and xenotime dated at 1977 +/- 14 Ma and 1984 +/- 13 Ma, respectively and also probably dates the collision between the Congo and Tanzania cratons. A fourth event represented by the intrusion of the Nyika Suite granites at 1944 +/- 7 Ma terminates the Palaeoproterozoic history. There follows a long time interval with no recorded orogenic history before the tectonic activity during the Neoproterozoic Pan African orogeny. The regional significance of the evolution of the Nyika Subdomain with respect to the adjacent Ufipa Subdomain and the "Bangweulu Block" to the west are discussed within the framework of the Ubendian orogeny and the wider Palaeoproterozoic history of the region.