Geochemical Evolution of Samoan Shield Volcanoes

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This project is for a geochemical and isotopic study of basalts and differentiated lavas of two Samoan shield volcanoes. This will be the first systematic evaluation of the full chemical stratigraphy of a Samoan shield volcano, and will provide an important comparison to several volcanoes studied in this way in Hawaii and Tahiti. The study can be accomplished using samples already in existing collections, but the PIs also have the opportunity to carry out some additional sampling and field studies in September, 1991. The effort will focus on obtaining new isotopic data on 20-25 additional samples selected on the basis of trace-element data, and acquisition of a much needed set of rare-earth abundances throughout the range of lava compositions. These will be particularly important to compare to analyses obtained by ion microprobe on clinopyroxenes in Samoan ultramafic xenolith and on lava phenocrysts. This award will also allow completion of a doctoral dissertation at Scripps Institution by Julie Dieu.