Single zircon evaporation and SHRIMP ages for granulite-facies rocks in the Mozambique belt of Tanzania

We report zircon Pb-Pb evaporation and U-Pb SHRIMP ages on high-grade gneisses from the Mozambique belt of eastern Tanzania in an attempt to understand the Neoproterozoic evolution of this belt. Several orthogneisses of granitoid composition have igneous emplacement ages between 2740 and 2608 Ma and document the presence of Late Archean crust of unknown dimension that is either part of the Tanzania craton farther west or constitutes a separate ancient crustal domain, perhaps related to Archean rocks in Madagascar. Paleo- and Mesoproterozoic ages, ranging from 1880 to 1095 Ma, are documented for granitoid gneisses in the eastern Usambara Mountains of northeast Tanzania, and the significance of these rocks in the geodynamic evolution of the Mozambique belt is equally uncertain. Ages between 843 and 665 Ma document a period of magmatic and depositional activity in the Neoproterozoic that is comparable to other parts of the Mozambique belt, notably Madagascar. Metamorphic zircons extracted from high pressure/high temperature granulite-facies ortho- and paragneisses yielded ages of ca. 640 Ma that we interpret to reflect the peak of regional granulite-facies metamorphism.