This project will focus on the Colorado Plateau and adjoining regions where an inferred Proterozoic-aged, peridotite root extends to a depth of approximately 80-100 km and is surrounded by rifted continental lithosphere. Abundant samples of the upper mantle occur in volcanic rocks on and off the Colorado Plateau, and some mineral phases in these xenoliths record the recent compositional history of the lithosphere. Trace element abundances (REE,Ti,Zr,Hf,Sr) of mineral phases will be used to deduce the variation in the bulk composition of the lithosphere vertically and laterally, the nature of the phases involved in recent magmatic or metasomatic events, the nature of any trace element fractionations (e.g., REE/HFSE) coincident with these events, and the timing of these events from modelling of zoning profiles. Principal analytical tools will be the ion and electron microprobes for in situ analysis of trace and major elements.
