The Galapagos volcanoes Sierra Negra and Alcedo represent two extremes of magmatic diversity. Sierra Negra is made up of compositionally similar, evolved tholeiitic basalts, whereas Alcedo has erupted a remarkable bimodal suite of tholeiitic basalts and oceanic rhyolites. It is believed that the difference in the extents of differentiation of these two volcanoes is related to fundemental differences in their magma chambers' histories, yet the two are so close that their flanks overlap. This project will perform detailed field, petrologic and geochemical studies of Alcedo volcano, in order to begin to elucidate these differences. Particular emphasis will be placed on determining the origin of the unique suite of oceanic rhyolites. Volumes of the different units, their eruptive order, and the locations of eruptions will be determined. These in turn will provide constraints on the petrologic processes that govern the evolution of oceanic magmas. Eventually it is planned to study Sierra Negra for comparison purposes, but such a study is not part of this project.
