Defining and Understanding Geochemical Heterogeneity in the Hawaiian Plume: Spatial and Temporal Geochemical Variations in Loa-trend Volcanoes

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Intellectual Merit: The geochemical differences between oceanic basalt erupted at submarine spreading ridge axes and islands reflect first order heterogeneity within the Earth's mantle. This heterogeneity results from major earth processes such as recycling of oceanic lithosphere into the mantle at subduction zones, recycling of continental lithosphere via delamination or continental breakup processes and melt/rock reactions, commonly described as metasomatism. The longterm preservation of such heterogeneity provides constraints on physical processes occurring in the mantle, such as convection, stirring and mixing. Especially important is evidence that different parts of a recycled system, such as oceanic sediments, upper and lower oceanic crust, lower continental crust are preferentially sampled at specific volcanoes for limited time intervals. Volcanism forming long-lived, age-progressive hotpot tracks, such as the Hawaiian Ridge, provides direct insight into the processes that form and maintain such heterogeneities. This proposal focuses on defining and understanding the origin of geochemical heterogeneity in lavas erupted at recent Hawaiian volcanoes. The rationale for studying Hawaii is that geochemical data for Hawaiian lavas can be interpreted within the context of an extensive framework of geophysical, geological and temporal constraints based on field studies including subaerial, submarine and deep drilling efforts. Such complementary information is lacking for other hotspot tracks. The research focus is on determining (a) the differences in incompatible element abundance and radiogenic isotope ratios that distinguish lavas forming the en echelon Kea and Loa trends of Hawaiian volcanoes, and (b) the variation of these geochemical parameters as an individual volcano evolves over time. Although Kea trend volcanoes, such as Mauna Kea, are well studied, similar data are not available for Loa trend volcanoes that have progressed through several volcanic stages. High precision geochemical data for lavas from Mahukona, West Molokai and Penguin Bank (all Loa trend volcanoes) will be obtained to define age-progressive geochemical trends. These data will be used to evaluate recently proposed models for the spatial arrangement of source heterogeneities, i.e. concentric radial zonation or bilateral asymmetric zonation. These alternatives carry very different implications for the physical processes that create geochemical heterogeneities.Broader Impacts: In terms of education and training as geochemists, the major impact is mentoring by Frey of two PhD graduate students. The research effort includes national (Woods Hole Oceanographic Institution and Monterey Bay Aquarium Research Institute) and international collaborations (Max-Planck-Institut fur Chemie and Ecole Normale Superieure de Lyon, France). These interactions expand the student horizons in that they interact with a larger group of scientists with diverse ideas, and they have access to analytical facilities not available at MIT. The research results and interpretations will be disseminated by presentations, dominantly by students, at national and international meetings and publications of research papers in international journals.