Hekla volcano in southern Iceland displays a remarkable correspondence between its style of volcanic activity and extent of petrologic evolution. Most eruptions are zoned, especially the ones that punctuate long repose, initiating with an explosive siliceous phase and ending with effusion of mafic icelandite. The pioneering work of Thorarinsson showed that the extent of differentiation at Hekla correlates with the repose between eruptions. This project is designed to study in detail the zoned products of the historical eruptions, in order to elucidate the mechanisms and timescales of differentiation. Field work will be conducted in order to collect sequences of samples from each historical eruption; because the eruptions are all historical, the minimum time for crystallization, mixing, and differentiation is well-constrained. Each of the rocks will be analyzed using modern, state of the art techniques, but the focus of this study is microanalysis of phenocryst phases, which are tracers of the liquid compositions from which they crystallized. Major and trace element zoning profiles of phenocrysts and analyses of melt inclusions will help determine the parentage of the phenocrysts, as well as the duration they have been entrained in their host magmas. Oxygen isotopic ratios of the phenocrysts and water analyses of melt inclusions record the extent to which water influences magmatic evolution. Finally, relatively short-lived actinide-series isotopic analyses of the phenocrysts will constrain their age, the amount of time they have resided in the magmatic plumbing system.
In terms of broader impacts, this award will support the research endeavors of a doctoral student at the University of Idaho and six Colgate University undergraduates. The PIs have designed a plan to provide the PhD student with teaching and mentoring experience working with the undergraduates on a protracted basis. The Colgate students, in turn, will have the opportunity to participate in extended fieldwork, interact with research scientists, work on independent, focused research questions. Results will also be incorporated into both undergraduate and graduate level courses at Colgate and the University of Idaho, as well as outreach programs designed to bring hands-on science investigation to local K-12 students and community groups.
