Volcanic rocks recovered by the Deep Sea Drilling Project from the Philippine Sea represent at least four stages of back- arc spreading and two episodes of volcanic arc building. Major and trace element studies of these samples have delineated important chemical differences between and among arc and basin lavas. The objective of the present award is to examine the lead, strontium and neodymium isotopes of these same samples. These data will be used to determine the extent of isotope variation among older basin and arc lavas and to identify geographic trends. Such information is important in defining the compositional range of mantle sources that contribute to arc and basin volcanism over time and in understanding the overall geochemical evolution of the arc-basin system. This project will be undertaken at an undergraduate institution.