Experimental studies will be carried out on basalt and andesite magma compositions from convergent plate margin environments. High pressure phase equilibrium experiments (up to 25 kbar) will provide compositions of magmas derived by melting mantle peridotite and allow development of models of the processes that modify these melts as they rise through overlying mantle into the crust. Experimental studies carried out at crustal level pressures will determine the compositional variations produced by fractional crystallization. These experimental studies provide constraints on the transfer of material from the upper mantle to the crust by volcanism in subduction zone settings. These studies also apply directly to the interpretation of calc- alkaline volcanic and plutonic rocks in the Cascades and Sierra Nevada. Field, petrologic and geochemical investigations at Medicine Lake Highland and Mount Shasta in northern California and Onion Valley, S. Sierra Nevada will use the experimental results to develop a framework for understanding the magmatic processes that lead to the compositional diversity of lavas and plutonic rocks in these calc-alkaline magmatic systems.
