9505771 Wyllie This project is aimed at understanding the origin and evolution of the siliceous magmas characteristics of batholiths in the roots of mountain ranges, and of orogenic volcanism, which involves the flux of materials through subduction zones and in other tectonic environments. Major efforts will be devoted to three specific geological problems, with new experimental data and the synthesis of these with experimental data from the several investigations of recent years. The three topics are: (1) the origin of early continental crust, (2) the conditions for partial melting of subducted oceanic crust: pelagic sediments and gabbro, and (3) the correlation of high resolution tomography in subduction zones with results from experimental petrology and thermal modeling.