This project is to continue studies of the temporal and petrochemical evolution of the Society Islands chain. Volcanic and plutonic rocks and upper mantle xenoliths have been collected to evaluate the parental magmas and differentiation mechanisms for alkaline oceanic islands and geochemical variations within these volcanoes. These studies will contrast with the better known, but perhaps atypical, tholeiitic Hawaiian volcanoes. Both lineaments are thought to arise from Pacific plate motion over stationary hotspots, and the contrasting geochemical evolutions should reveal complexities in hotspot structure and possible melt contributions from the oceanic lithosphere. Over 150 samples collected from two volcanoes on the island of Tahiti have been described petrographically and their ages determined. These investigations will now be extended to other volcanoes in the Society Islands and will involve a collaborative program of radiometric, geochemical and esperimental studies at Oregon State, and isotopic analyses by William White at Cornell. A large number of new samples and geological maps are being supplied by French volcanologists R. Brousse and H. Barsczus.
