Lithium Isotope Compositions of Hawaiian Lavas: A Study of Source Components

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9903197ChanThe Hawaiian chain is an important example of hot spot volcanism. Shieldlavas exhibit considerable variation in chemical and isotopic composition.The compositional diversity reflects distinct source components in themantle and interaction of the mantle plume with lithosphere and the uppermantle. This project introduces lithium isotopes as a new isotopic tracerfor the study of ocean island basalts. Recent developments of massspectrometric techniques have led to precise characterization of lithiumisotope compositions of marine reservoirs. Lithium isotopic data ofseawater, fresh and altered ocean crust, marine sediments, and mantleperidotite are available to evaluate the origin of Hawaiian lavas. Theproposed study will focus on lavas from four volcanoes: Koolau, Mauna Kea,Mauna Loa and Kilauea. Koolau and Mauna Kea are considered to be extremecompositional endmembers in Hawaiian volcanoes. Isotopic evidence suggeststhat Koolau lavas represent plume material enriched with recycled oceaniccrust and sediments , whereas Mauna Kea lavas has incorporated melts ofrecycled hydrothermally altered lower crust. The objectives of the lithiumisotope study are to identify source material in the Hawaiian plume,including recycled components from the subducted oceanic lithosphere andsediments, and to trace the isotopic evolution of the magmas with timeusing drill core samples. In a broader sense, this study addresses theissues of isotopic heterogeneity in the mantle, melt-lithosphereinteraction, and recycling of subducted crustal material.