Fractional crystallization is one of the most important yet most poorly understood of all igneous petrologic processes. One key to understanding how fractional crystallization operates is through the study of magmatic cumulates generated during a composition gap-forming event. This study will include detailed textural (Universal-Stage), geochemical, micro-probe and, most significantly, ion-probe investigations of the Medicine Lake cumulates. Textural studies will concentrate on the degree of preferred mineral orientation. Geochemical studies will characterize the major and trace element variability in both the cumulates and associated magmas. Micro-probe and ion-probe studies will determine major and trace element zonation styles in individual cumulate minerals, as well as the degree of sympathetic compositional variation among neighboring cumulate minerals. Altogether, these complimentary lines of evidence will be used to assess the physical nature of fractional crystallization at Medicine Lake and, by inference, in other calc-alkaline magmatic systems of similar style.
