Osmium Isotope and Highly Siderophile Element Abundance Studies of Mantle Sources Sampled by Ocean Island Basalts

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Osmium isotope and highly siderophile element abundance studies of mantle sources sampled by ocean island basaltsIntellectual merit of the proposed activity: This project will address the fundamental question of whether fractionation of highly siderophile element (HSE = Os, Ir, Ru, Rh, Pt, Pd, Re, Au) and Sr-Nd-Os-Pb isotopes can be used to identify unambiguously recycled or primitive materials present in some ocean island basalt (OIB) mantle sources. Data for Hawaiian and western Canary Island lavas suggest this is possible, but more data are required to test this hypothesis fully. Understanding of HSE behavior in the mantle, and in the sources of OIB in particular, is limited, and Os isotope data are lacking for many OIB samples for which Sr-Nd-Pb isotope data are available. Collection of new Os isotope and HSE abundance data on OIB lavas is therefore an important task for better understanding of mantle heterogeneity. The project will; (1) provide further constraints on the range of variation of 187Os/188Os in OIB mantle sources; (2) establish whether Os isotopes and HSE abundances can be used to constrain recycling of crust and lithosphere back into the mantle; and (3) better define the distribution of HSE in OIB mantle sources. Suites of lavas from the eastern Canary Islands (La Gomera, Tenerife, Gran Canaria, Fuerteventura, Lanzarote), Cook Islands (Mangaia, Atiu, Rarotonga), and Mascarene Islands (Réunion, Mauritius) will be systematically examined for petrology, mineralogy, whole-rock major- and trace-element abundances, HSE (Os, Ir, Ru, Pt, Pd, Re) abundances, and Sr-Nd-Os-Pb isotope systematics using state-of-the-art analytical techniques. These islands were selected for study because there is strong prior evidence for recycled (Canary Islands, Mangaia, Atiu) or primitive (Mascarene Islands; Rarotonga) material in their mantle sources, and appropriate samples are in hand for this study. New data will be used to assess effects of crustal contamination versus mantle heterogeneity, and to model the nature and proportions of recycled material in local mantle sources. Broader Impacts of the proposed activity: Components of training and teaching are a strong theme of the proposal, with direct involvement of graduate and undergraduate students. The project will serve as the core of a PhD thesis for a graduate student, and will equip a number of undergraduates with highly transferable quantitative analytical and communication skills. Students involved in this project will gain extensive experience in several state-of-the-art analytical techniques, and the graduate student will participate in fieldwork, receiving training in field methods. This proposal will also support a recently appointed early-career non-tenured Assistant Professor (start date, January, 2011). Research results will be incorporated into classroom lectures and in inquiry-based learning activities at Scripps Institution of Oceanography. Outreach for the project will include contributions at both scientific and public-domain levels, through educational website material, and in talks at high schools and public events in the San Diego area.