9506597 Newsom This project will use the fluid/sediment sensitive siderophile trace elements Pb, As, Sb, as well as the fluid sensitive trace element B, to examine the variations in lava chemistry from arc transects in selected oceanic and continental arcs, and from volcanoes east and west of the Quesado Sharp Contortion (QSC) in north-central Costa Rica. Complementary data will be collected from samples derived from the mantle, including Mid-Ocean-Ridge Basalts (MORB) from depleted mantle, Ocean Island Basalts (OIB) from enriched mantle, and rift and flood basalts (including samples for Franz Josef Land, Russia) from the asthenosphere and continental lithosphere. The concentrations of Pb, As, Sb and other siderophile elements will be determined by Inductively Coupled Plasma-Mass Spectrometry (CP-MS) at the University of New Mexico, while B, Be and Li data will be obtained by our collaborators. The enrichments of Pb, As, Sb, and B in volcanic arcs and the continental crust can not be attributed to igneous fractionation alone based on inferred partitioning between mantle minerals and basaltic melts. These enrichments can, however, be attributed to the addition of a fluid/sediment subduction component to the magma source region. The enrichments provide an important signature of the involvement of subduction zone volcanism in the formation of the continental crust.
