Collaborative Research: MARGINS--The Relationship Between Water, Trace Elements and Slab Dehydration Across the Mariana and Izu-Bonin Arcs

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Intellectual Merit. The role of water in subduction zones is largely understood based on behavior of fluid-mobile elements such as B, Ba, K, Rb and U, rather than on measurements of water directly. This is because most studies of arcs rely on data from subaerial lavas which have suffered volatile loss through degassing. Published experimental studies and melt inclusion studies across the Central American arc suggest that water is released continuously from the slab across the arc. This is contrary to the behavior of fluid mobile elements, which are progressively stripped from the slab and show systematic cross-arc changes. A fundamental aim of this study is to evaluate the release of water, trace elements, and stable isotopes of hydrogen and boron across two contrasting segments of the IBM system - the Marianas and the Izu-Bonin arcs. These sites have different dip angles and subduction rates, thus we will determine whether these physical parameters have any impact on fluid behavior during progressive dehydration. The second objective of this study is to test how well trace element and B-isotopic proxies for slab fluids track fluid delivery to IBM mantle sources, and whether D/H and B isotopes trace similar fluid release processes or whether each system uniquely traces different stages of dehydration. We propose a systematic study of volatiles (CO2, H2O, S, Cl, and F), fluid soluble elements (B, Cl, Ba, K, Rb and others) and stable isotopes (H, B) in glasses and olivine hosted melt inclusions (MIs) from submarine lavas using ion microprobe techniques. This work will be complemented by multicollector ICPMS analyses of B isotopes, as well as electron microprobe measurements of major elements. The samples include a new suite of cross-chain volcanoes from the Marianas, back-arc lavas and glasses from the Mariana Trough, and lavas from the Izu-Bonin arc and back-arc. The correlation (or lack thereof) between arc magma water contents and fluid-mobile trace elements will have an important impact on the interpretation of geochemical signatures at other subduction zones with existing trace element and isotopic data but where water contents have not yet been measured.Broader Impacts. This project will complement ongoing MI studies investigating the melting process in the Lau Basin, as well as the scientific objectives of the MARGINS Subduction Factory initiative, and will foster collaboration between scientists at five institutions in the US and Japan. The project will support a female early career scientist at Woods Hole Oceanographic Institution (WHOI). As part of a WHOI and NSF-REU summer intern programs, the PI will mentor an undergraduate student during the 2nd year of the project, introducing them to ion microprobe techniques. This work will also result introduce new analytical protocols to help revitalize the NSF-supported WHOI ion probe facility which was seriously damaged in a fire in October of 2002.