Li Isotope Studies of Mantle Xenoliths From the SW USA

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SIMS measurements of 7Li/6Li in minerals from peridotite xenoliths will be performed in order to understand the origin of Li isotope heterogeneities in mantle samples. The spatial distribution of 7Li/6Li will be determined in relation to (i) grain boundaries and cracks of individual mineral grains and (ii) metasomatic veins and xenolith margins of individual xenoliths. The relationship of 7Li/6Li to major and trace element composition of minerals, determined by electron microprobe and SIMS, will be investigated. These measurements will be used to assess the influence of different types of metasomatism on Li isotope composition of the mantle, and the extent to which volcanic emplacement processes modify mantle Li isotope signatures. Li concentration and 7Li/6Li of hydrated Colorado Plateau and nominally dry Basin and Range mantle samples will be compared to investigate transport of Li by hydrous fluids in the mantle. It is anticipated that the results will contribute to understanding global Li geochemistry, the use of Li isotopes as a tracer of recycling and fluid processes in the mantle, and the role of mantle fluids in the tectonic evolution of the SW USA. Broader impacts include development of SIMS analytical methods and inter-laboratory collaboration on Li isotope analysis with the University of Maryland, and training for a graduate and an undergraduate student. Scientific results and student participation will be integrated with Earthscope. Field work will aim to engage Native American students in Earth Science and contribute to new initiatives at ASU in geoscience education for indigenous learners.