This is for continued support of three separate programs of research in radiogenic isotope geochemistry as applied to hydrothermal processes, silicic magma systems and mantle geochemistry. 1. The research in hydrothermal processes will emphasize the further development of techniques for determining the timing and scales of fluid movement. These techniques may include dating of fluid inclusions, dating of sulfides, dating of carbonates, phosphates and accessory mineral overgrowths, and REE analysis of a variety of hydrothermal phases including sulfides and fluorite. Research will be concentrated on MIssissippi Valley Type (MVT) deposits and pluton-related mineralization in the U.S. and U.K. 2. Studies of silicic magma systems will focus on dating of magma differentiation using Rb-Sr techniques, the longevity of magma chamber residence by resolving differentiation ages from eruption ages, and the study of mass transfer within silicic systems. A number of systems in the U.S. and elsewhere have been chosen for study. 3. Current research on the geochemistry of the mantle under the Cameroon line is to be expanded to study trace element enrichment processes as a function of lithospheric age using lavas and/or ultramafic xenoliths from various volcanic centers. In addition, techniques for dating young MORB using 40Ar-39Ar are being developed.
