The Mecubúri and Alto Benfica Groups, NE Mozambique: Aids to unravelling ca. 1 and 0.5Â Ga events in the East African Orogen

The detrital zircon data from the Alto Benfica Group suggest that the Nampula Complex was juxtaposed with the adjacent terranes of northern Mozambique and SE Africa, which were uplifted, exposed to sub-aerial weathering and locally lateritised at the time of deposition. The terrane juxtaposition event can be equated with the main, NW-SE-directed collision phase of the East African Orogeny at ca. 550 Ma. The resulting mountain belt was rapidly eroding and providing detritus for the two clastic sequences at ca. 530 Ma, probably during the early phases of extensional orogenic collapse. Later in the extensional phase, local SW-NE oriented compression deformed the Mecubúri and Alto Benfica Groups, along with the basement, into tight upright folds, with associated axial planar foliation. Sillimanite-grade metamorphism and migmatisation, associated with the emplacement of late-tectonic granites took place at ca. 500 Ma. It follows that none of the regional fabrics and large-scale structures in the Nampula Complex are Mesoproterozoic in age; the present distribution of lithological units and structures are almost entirely the result of the East African collisional orogeny at ca. 550 Ma and its subsequent extension and collapse.