Boron isotopic ratios will prove useful in clarifying the source of B and the processes by which it is incorporated into arc magmas. This project is to analyze basaltic lavas from a number of volcanic arcs to establish correlations with such factors as subduction rates, thermal state, geometry, etc. For comparison, selected lavas from within-plate settings (Ocean islands and spreading centers) will be analyzed to better define the B isotopic composition of mantle regions that are unaffected by subduction. Also it is planned to analyze samples from two progressive metamorphic suites to evaluate isotopic fractionation effects accompanying dehydration and recrystallization. The proposed work is relevant to studies of fluid-rock interaction and mass transport via hydrothermal brines, to tracer studies of subduction-related processes, and to studies of the evolution of hydrothermal mineral deposits and effects of prograde metamorphism on devolatilization of crustal rocks.
