Accomplishment Based Renewal: Geochemical Evolution of the Mantle

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Melting processes driven by flow within the Earth determine the character and hazard level of volcanic activity. This research targets improving our understanding of the mantle dynamics that control hotspot lineations and the associated melting processes that control subsequent volcanism. This will involve an isotopic study of peridotite xenoliths and melt inclusions in phenocrysts from a number of volcanoes in the Samoan Island chain, using in situ ion probe and laser ablation-ICP/MS techniques, as well as assimilating information from tectonic constraints. Results of the research will shed light on the genesis, evolution, placement and lithologic nature of chemical heterogeneities in the Earth and the dynamics of melting and melt extraction from these domains. It also addresses whether the Samoan hotspot is a manifestation of a deep mantle plume. One hypothesis to be tested is whether rejuvenated volcanism in the Samoa area is related to the migration of the tear in the subducting Tonga slab as it rolls back to the east. Comprehensive geochemical studies and dating of basalts from seven of the islands and seamounts will be used to test whether this is the case. Broader impacts of this work include the support of graduate student and support of analytical infrastructure in terms of the clean lab/mass spectrometer isotope facility at the Woods Hole Oceanographic Institution (WHOI) in Massachusetts, which is used as an open-door laboratory facility by many members of the geoscientific community. Over the last three years this facility has provided analytical expertise and infrastructure for more than 32 students and staff, about half from WHOI and half from other institutions. New analytical protocols devised during the award period will be posted for public access on the Internet. Funding will also help complete a seismic study of the Samoan Islands, in which Samoan high school students and teachers are trained in the running, operation, and maintenance of seismic stations. The seismic work will also be incorporated into their class work. This PI will also help run a 3-week workshop at the Cooperative Institute for Deep Earth Research to bring together faculty and students from seismology, mineral physics, geochemistry and geodynamics.