Recent studies have demonstrated that certain arc volcanic rocks are enriched in 10Be and B derived from subducted oceanic crust and sediments. Because the host phases for these elements are unknown, we propose a systematic ion microprobe investigation of high pressure- low temperature metamorphic rocks in order to determine the distribution of Be and B among mineral phases stable under subduction zone conditions. Specifically, we will determine (1) which phase are responsible for the Be and B signatures of the subducting slab, (2)Be and B partitioning coefficients for different mineral pairs, and (3) the variation of Be and B distribution as a function of metamorphic grade. Analyses of synmetamorphic migmatites and host rocks from the Catalina Schist, a pale-subduction zone, will place constraints on the behavior of Be and B during melting. Analyses of syn-and post-metamorphic vein minerals will place constraints on the mobility of Be and B in aqueous fluids. We will also evaluate the possibility that Be and B reside in poorly- characterized phases along grain boundaries. As in our previous studies, we will continue to collect data on other elements including H, Li, and selected REE. The results of the proposed investigation will increase our understanding of subduction zone processes and arc magmatism.
