It is generally agreed that fluids play a critical role in mantle enrichment processes and that mantle enrichment events frequently are superimposed in a complex manner on peridotitic mantle that has been depleted in incompatible trace elements and light rare- earth elements through prior partial melting. Chemical and radiogenic isotope data suggest that such metasomatic fluids may be derived, in part, from recycled crustal materials and that some form of fluid metasomatism may be a necessary precursor to intraplate alkalic magmatism. Stable isotope studies provide a unique means of addressing mantle heterogeneity and enrichment/depletion processes because, 1) oxygen is a major element in terms of its behavior, whereas hydrogen is a trace element that is concentrated in aqueous fluid phases, and 2) the mantle has been shown to be heterogeneous in terms of both its O- and H-isotope compositions. This project will undertake a detailed stable isotope study of four regions in which mantle peridotites of distinctly different petrological, chemical, and radiogenic isotope character have been erupted in Late Tertiary to Recent alkalic basalts. The four gerions also are characterized by having sub-continental lithospheric mantle with differing tectonic histories. The focus of the research is an understanding of the causes of stable isotope variations in the different types of peridotites present within each region, and a comparison of the isotope systematics of peridotites from the four gegions in the context of their different tectonic histories.
