Temporal/spatial scales of mantle wedge composition and processes investigated with young boninites and basalts from the unusually active NE Lau Basin

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This project is a study of subduction zone volcanic rocks to understand how they form. Subduction zones are places where materials from Earth's surface (sediments, volcanic rocks, and other rocky materials) are returned to the mantle. During this process fluids are drawn from the "slab" of subducting material while it descends, causing the overlying mantle to melt, producing magmas that drive a significant portion of Earth's volcanism. Despite 50 years of research about how and where this magmatic activity occurs, the range of volcanic styles and products, and their contributions to human society (hazards, ore formation, landscape evolution, etc.), numerous questions remain about the conditions and timescales of melting in the mantle, the different types of rocks that might melt, and the sizes and shapes of these different subterranean rock regions. In addition scientists still have a very incomplete picture of how all of these things contribute to what type of magma is ultimately erupted and what style the eruptions take (for example, how big, how frequent, how explosive). This research project addresses these questions using recently erupted, rare, volcanic rocks called boninites. These rocks form when H2O is added to the shallow mantle under very high temperature conditions. The tools of geochemistry, isotope geochemistry, and naturally-occurring radioactive element distributions in these rocks will be used to analyze an already existing, unique, set of samples. Project goals are to determine: (1) the variety and spatial scale of mantle compositions beneath this subduction zone, (2) the timescales over which they melt, (3) how magma forms and migrates to the surface, and (4) how this contributes to volcanic activity. Answers to these questions have broader impacts to society and the national interest because they provide information on processes leading to magmatism and volcanism (and associated hazards and benefits) at subduction zones, which occur both off the western coast of the United States and along the coasts of many of our partner nations in the Americas, Caribbean and Pacific Rim, like Japan, Taiwan and New Zealand. In addition, the project will fund an institution in an EPSCoR state (Hawaii), support an early career researcher, and carry out public outreach through the NOAA outreach engine and U Hawaii websites. This project will study interoceanic subduction zone volcanism, using a unique set of young boninite and related mafic/ultramafic samples from the nine Mata Volcanoes and neighboring rear arc and back arc volcanoes (Northeast Lau and Fonualei Spreading Centers). U-series disequilibria and analyses of Sr-Nd-Pb-Hf isotopes, and major/trace element abundances in already-collected volcanic glasses, minerals and whole rocks will be used to investigate high resolution (km-scale) mantle wedge heterogeneity at an active inter-oceanic arc/backarc, sub-millennial variations in subduction fluid inputs, and conditions of boninite and other magma petrogenesis. Hypotheses will be tested to address how fluids from the subducting slab induce melting in the overlying mantle, how different compositions of mantle melt, how different magmas are delivered to the surface in a way that preserves large variations in magma composition over small spatial scales, and the timescales of these various processes, which prelimimary data indicates is likely to be much faster in some cases than heretofore realized.