9725351 Hauri This is a geochemical and geochronological study of volcanic islands and seamounts comprising the Austral Islands chain of French Polynesia. This chain is being studied in order to determine whether the Hawaiian model of a focused, narrow mantle plume is an adequate one for describing all aspects of the actively convecting part of the Earth's mantle. The Austral Islands are differ in almost every aspect from the Hawaiian islands. New Ar-Ar dating of lavas and seamounts will be combined with plate-motion reconstructions using Pacific pole of rotation fixed by the Hawaiian and Louisville hotspots to determine if the size of the Austral anomaly is consistent with a narrow plume, a sheet, or a leaky plate over a diffuse warm-spot. Combined geochemical studies on lavas, xenoliths, and melt inclusion will address several key questions regarding the coupled morphologic and geochemical variation across the Austral Fracture Zone including what role the oceanic lithosphere plays in the style and composition of the Austral volcanism. The combined Os, O and He isotope studies will help determine if the chemical characteristics of the Austral HIMU and EM sources are more consistent with crustal recycling or intra-mantle metasomatism.
