Compressional reworking of the East African Orogen in the Uluguru Mountains of eastern Tanzania at ~550 Ma: implications for the final assembly of Gondwana

The Uluguru Mountains of eastern Tanzania represent a key area to unravel the tectonic history of Gondwana assembly along the Neoproterozoic East African Orogen. On the basis of combined structural and 40Ar/39Ar geochronological investigations, we have re-interpreted the structural architecture of the region. Texturally-late, ductile to cataclastic low-angle tectonic contacts are recognised, which delimit the contacts between the main lithological units that form a post-metamorphic, NW-verging nappe stack. 40Ar/39Ar geochronology places this nappe-forming event at about 550 Ma, post-dating tonalitic dyke emplacement at about 580 Ma. Results from this study (i) demonstrate that a distinct and later episode of convergence occurred in the region at about 550 Ma, when previous structural elements of the East African Orogen were finally juxtaposed; and (ii) allow to extend models involving the polyphase assembly of Gondwana to East Africa