The Mantle Melt Column and Melt Migration Revealed by Deglaciation Melting Beneath Iceland's Western Rift Zone

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Magma that feeds volcanic eruptions on oceanic islands and most of the deep ocean is produced by melting of the underlying mantle. Current knowledge of the details of magma genesis and transport are derived from observations of eruption rates and basalt chemistry coupled to numerical modeling. However, because the products of volcanic activity usually provide only a time-integrated view of the melt migration process, it is normally very difficult to constrain the important rates and time scales of melt transport. This project will exploit the unique situation of time-varying melting perturbations due to glacial unloading in Iceland to provide unprecedented constraints on aspects of mantle melting that will be applicable to mantle melting studies in a wide range of geological settings. The project has a significant international component involving collaboration with the University of Iceland. It also has a major educational and training component for a young scientist who will have recently obtained her PhD at the University of Hawai'i. With this project she will gain experience in field mapping and Icelandic geology and volcanology as well as learn new techniques in a range of geochemical analyses and in sophisticated geodynamic modeling. The project is intended to involve undergraduate students from the University of Hawaii in the field work and follow-on research. The proposed research will enrich teaching and research programs at the University of Hawaii, which is located in an ethnically diverse community, including people from a range of Asian and Pacific island countries. It will therefore provide advanced technological training and mentoring of science students with diverse cultural backgrounds. Theory and preliminary observations indicate that the removal of ice at the end of the last glacial period profoundly affected volcanic production and magma chemistry in Iceland. The project investigators will constrain the timing of glacial retreat using ice core data and geologic reconstructions for the period between 15 and 11 thousand years before present. They will use new geologic mapping and sample collections, geochemical analyses, and 3He exposure age dating of subaerial lavas that surmount late-glacial table mountains to extend the record of eruption rates and lava composition back to 15 ka. Numerical models will simulate the updated glacial unloading history as well as the resulting perturbations to mantle melting, melt migration, and chemical transport. By modeling the observed temporal variations in eruption rate and trace-element and isotopic compositions, they will constrain the rates of melt transport, determine basic properties of the mantle melt column, and test for the presence of small-scale mantle heterogeneity.