9628251 Feigenson This project will focus on providing constraints on the geochemical character of island-arc volcanoes in Central America. Previous work in Central America has indicated that the volcanoes in northern Costa Rica and southern Nicaragua display geochemical compositions that are consistent with a transition between two mantle terrains with different geological histories. The first part of this study will focus on the Pb isotopic composition of the lavas from the vents along this portion of the arc with the purpose of defining this mantle terrain boundary and to evaluate if the underlying mantle was affected by the passage of this portion of the plate over the Galapagos hot-spot at about 90 million years ago. The second objective of this study will be to measure the temporal variation in the subduction signature over the last 2-3 my at the segment of the arc immediately onshore by analysing a core of sediments (DSDP 495) for Ba/La, B/La, U/Th, Ba/Th and U/La. This will provide basic stratigraphic and geochemical data necessary to develop realistic models of recycling of sediments through to the mantle at convergent margins.
