By thorough examination of the spatial variations in textures, mineralogy and chemistry in a few recent, well-characterized ash flow sheets, the PIs will be able to determine the systematics of devitrification and vapor- phase alteration and to develop a model for these processes that will allow them to predict their role in element redistribution. These textures are usually too fine-grained to be adequately characterized by standard optical petrography, therefore 'nanopetrography' studies will be performed using analytical transmission electron microscopy (TEM) in addition to standard mineralogical methods of characterization, in order to determine the mechanics and systematics of devitrification and vapor-phase alteration. These studies should lead to three seperate publications, providing significant new information on the evolution of silicic volcanic rocks.
