Collaborative Research: Chemical, Isotopic and Volatile Constraints on the Evolution of the Lau Basin

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Intellectual MeritThis research supports four investigators at two southern California universities to carry out a comprehensive geochemical and isotopic investigation of magmatic processes occurring in the Lau back-arc basin in the western Pacific. The setting is an ideal one to study and understand links between subducting oceanic crust and its sediment cover, back-arc mantle dynamics, and heterogeneity as well as the mantle source of magmas erupting along the arc and on the seafloor. This work seeks to characterize the geochemistry of the mantle beneath the basin and discern its control on basin evolution. In particular, the research will focus on understanding how the composition of the ocean crust in the Lau Basin in the western Pacific Ocean is affected by materials coming from the Pacific plate that is being subducted to the east. The Lau Basin has been a site of intense reconnaissance work and the targeted geochemical sample suite consists of 400 lavas and glasses collected by Scripps Institution of Oceanography during five NSF-sponsored cruises to the region. The sample inventory represents extensive coverage of the Lau Basin, including lavas from all recognized spreading centers. This research will analyze representative igneous and volcanic rocks for major and trace element chemistry (including REE, HFSE, and light elements Li, Be, B, Cl); volatile elements (CO2, H2O); isotopes of Sr, Nd, Pb, Hf, He, Ne, and Ar; and short-lived isotopes of the U decay series (226Ra, 230Th, and 234U). With this unprecedented data set, the research will be able to address the following four issues: (1) whether it is possible to map the spatial distribution and extent of Indian- and Pacific-type mantles in the Lau Basin; (2) what the spatial extent of the Samoan mantle plume component in the Lau Basin is; (3) how the proximity of the Lau Basin spreading centers to the Tofua Arc affects mantle melting, and (4) what proportion of volatile enrichment in Lau Basin lavas is due to ridge-arc source interaction versus other processes such as crustal assimilation. This work will provide the framework for additional work in the region. The work is important for the science objectives of the NSF-funded MARGINS and RIDGE 2000 Programs. Broader Impacts: Broader impacts of this research include contributions to education and training of at least three graduate students (Ph. D. and/or M.S). Furthermore, undergraduates will be involved in selected aspects of the work. Students will receive broad geochemical training in a number of sub-disciplines of analytical geochemistry. In addition the presence of PhD-level students from the University of California, San Diego (UCSD) at San Diego State University (SDSU), which has no PhD program, will stimulate and challenge the undergraduate and Master's students to higher levels of achievement. Finally, the proposal will help to support the considerable analytical infrastructure at UCSD and SDSU, as well as foster closer working relationships between faculty and students at both institutions.