Lithium, boron, and lead isotope systematics of glass inclusions in olivines from Hawaiian lavas: evidence for recycled components in the Hawaiian plume

Abstract

Lithium (Li), boron (B), and lead (Pb) isotopic compositions of glass inclusions in olivine phenocrysts from Hawaiian lavas, (Kilauea Iki, Mauna Loa, and Koolau volcano) were measured by high mass resolution ion probe to search for possible signatures of recycled materials in the Hawaiian plume. In order to measure the isotopic compositions, a set of synthetic glass standards with matrices similar to those of the target glass inclusions was prepared. Isotopic variations among these synthetic standards were produced by additions of spikes, and their isotopic compositions were determined by TIMS. Using this set of standards, correction factors for instrumental mass fractionation for Li, B, and Pb isotope measurement were determined with internal precisions of <1.2‰, <1.6‰, and <0.8% (2 σ) uncertainties for Li, B, and Pb, respectively. Twenty-eight glass inclusions were measured after homogenization to eliminate dendritic crystals. These glass inclusions showed isotopic variations from −10.2‰ to +8.4‰ for δ 7Li, from −10.5‰ to +5.2‰ for δ 11B, from 0.7994 to 0.8909 for 207Pb/ 206Pb, and from 1.989 to 2.139 for 208Pb/ 206Pb, which are considerably larger than those for whole rocks. This suggests that the Hawaiian lavas are mixtures of melts derived from isotopically distinct sources, and that glass inclusions better preserve information regarding source heterogeneity than do whole rocks. In particular, significantly low δ 7Li and δ 11B values for the Mauna Loa and Koolau samples indicate an isotopically “light” Li and B source, perhaps containing recycled materials that experienced dehydration during subduction. The extremely low Pb isotope signature, which corresponds to HIMU, also suggests some contribution from recycled materials to the generation of the Hawaiian magma. Our results suggest that recycled materials, which experienced near-surface alteration and then dehydration during subduction, played an important role in creating geochemical heterogeneity in the Hawaiian lavas.