The P.I.s to study the 10- to 5-Ma segment of silicic volcanism along the High Lava Plains. The first stage, the subject of this project, is a comprehensive mapping and high- precision 40Ar-39Ar dating study, supplemented by reconnaissance geochemical analyses of mainly the silicic volcanic rocks. A later stage will be aimed at the petrologic evolution of the silicic volcanic rocks, as warranted. The principle aims are: (1) to examine in detail the regional northwestward age progression of silicic volcanism, and to investigate whether age-progressive trends within silicic centers mimic the regional trend; and (2) to evaluate the composition of the silicic volcanic rocks as a function of space and time by geochemical analyses of date and (or) stratigraphically controlled samples. This will provide an unique series of time-composition slices through the evolution of a silicic volcanic province and will be a foundation for comparison to silicic volcanism along the Snake River-Yellowstone trend.
