This project will continue geochemical studies of lavas of known relative age from several Hawaiian volcanoes, the eastern active zone of Iceland, and a miocene basaltic plateau in eastern China. A major objective is to understand the origin and evolution of interplate lavas because "hot-spot" volcanism is the major type of volcanism which is not an obvious result of plate tectonics. Moreover, in each of these areas there is a transition from tholeiitic to alkalic compositions and a specific objective is to determine the cause of these transitions in different tectonic settings. In Hawaii it is planned also to identify and interpret geochemical variations within and between tholeiitic shields. This is an important objective because previous results show clearly that the plume component is most evident in the shield tholeiites, but little information exists about the temporal evolution of these shields. The approach will be to constrain the mineralogy and composition of source components from study of the lavas and where present, the peridotite xenoliths. Field relationships, major and trace element analysis of whole rocks and minerals, and isotopic analyses (Sr, Nd, Pb) will all be used. Models will then be developed using more complex melt segregation concepts.
