Elsevier, Earth and Planetary Science Letters, 3-4(266), p. 316-331, 2008
DOI: 10.1016/j.epsl.2007.11.020
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We report Li concentrations and isotopic compositions for olivine and pyroxene separates and bulk rocks of variably metasomatised harzburgite xenoliths hosted by andesitic tuffs of the active Avacha volcano in the Kamchatka arc, and for a single lava-hosted harzburgite from the intra-plate Vitim volcanic field, Siberia. The Li-isotope data on the Avacha samples (δ7Li = 0 to + 5‰) mainly fall within the range reported previously for ‘normal’, MORB-type mantle (+ 2 to + 6‰) and show no significant inter-mineral disequilibria. These results indicate that the shallow mantle in the active Kamchatka arc, and probably in other subduction zones, has roughly (i.e. within ± 2‰) MORB-type Li isotopic signatures. By contrast, pyroxenes from the Vitim xenolith yield extremely low δ7Li (− 17‰ and − 18‰) and are out of equilibrium with coexisting olivine, which has high δ7Li (+ 6‰). Taken together, these results indicate that anomalous Li elemental and isotopic compositions in mantle xenoliths cannot be considered signatures of shallow sub-arc mantle or evidence for recent or ancient slab-related metasomatism.