One feature of arc and back-arc basin volcanic systems isthe close juxtoaposition of lavas of radically different compositions that are derived from apparently different mantle sources. One of the problems in understanding these systems is defining the types and proportions of different sources contributing to that diversity of magmas. This project will sysematically sample the active back-arc spreading center and the extinct arc to obstain a better representation of the temporal and spatial distribution of this source beneath the Marianas Islands arc. Fundmental questions to addressed are: what are the principal components contributing to magmas in island arcs and back-arcs, how do these sources mix and interact spatially and temporally, and what can be deduced about the geometry of the sources from that mixing?
