Li Isotope Studies of Mantle Xenoliths From the SW USA

为了了解地幔样品中Li同位素不均匀性的成因，将对橄榄岩捕虏体矿物中的7 Li/6Li进行西姆斯测量。7 Li/6Li的空间分布将根据（i）单个矿物颗粒的晶界和裂纹以及（ii）单个捕虏体的交代脉和捕虏体边缘来确定。用电子探针和西姆斯法研究了7 Li/6Li与矿物主量和微量元素组成的关系。这些测量将用于评估不同类型的交代作用对地幔锂同位素组成的影响，以及火山侵位过程在多大程度上改变地幔锂同位素特征。Li浓度和7 Li/6Li的水合科罗拉多高原和名义上干燥的盆地和山脉地幔样品将进行比较，以调查在地幔中的含水流体的锂的运输。预计这些结果将有助于了解全球锂地球化学，使用锂同位素作为示踪剂的回收和流体过程中的地幔，地幔流体的作用在构造演化的西南美国。更广泛的影响包括西姆斯分析方法的开发和与马里兰州大学在锂同位素分析方面的实验室间合作，以及对一名研究生和一名本科生的培训。科学成果和学生参与将与地球镜相结合。实地工作的目的是让美国土著学生参与地球科学，并为亚利桑那州立大学为土著学生提供地球科学教育的新举措做出贡献。

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.