Oxygen and hydrogen isotopic composition and zircon morphology of some Pan-African granites

The Pan-African orogeny took place throughout the Late Proterozoic and Cambrian time. Its final stage (c.500 Ma) is evidenced by radiometric age determinations. A set of samples from Pan-African granites collected from the Gondwana supercontinent (West Africa, East Africa, Brazil and Antarctica) were studied for their oxygen and hydrogen isotopic composition and zircon morphology. The purpose of this study was to obtain further information on the genesis and geochemical history of these granites. As regards the isotopic composition of single phases, the results generally point to equilibrium conditions. The temperatures obtained from phase-phase equilibrium equations are close to 500°C. The zircon morphology, on the other hand, points to a major role of water activity in the evolution of these granites which, in the light of isotope data, must have taken place at T above 500°C. -from Authors