9405310 Dyar This research seeks to examine the interrelationships among Fe3+, H+, and bulk composition of coexisting mantle minerals from within a carefully-constrained geologic context. Samples will be selected from Rio Grande rift and Colorado Plateau localities which will be the sites of A U.S.G.S. multidisciplinary transect planned for 1995. We plan to characterize Fe3+/ Fe ratios and H+ of all coexisting minerals in mantle xenoliths collected from the chosen localities, in order to determine regional variations in mantle redox conditions along the transect. We will also study metasomatic redox processes in composite mantle xenoliths with emphasis on observing redox differences and similarities between cryptic and patent metasomatism. H+ contents of all coexisting minerals in both unmetasomatized and composite metasomatized xenoliths will be measured; when possible, D/H ratios will also be determined in order to better understand the role of H+ in mantle redox processes.
