Oxygen isotopes in Samoan lavas: Confirmation of continent recycling

Abstract

Lavas from the Samoan volcanic chain show the most enriched geochemical signatures ever documented in oceanic lavas (⁸⁷Sr/⁸⁶Sr as high as 0.7205). In order to test the hypothesis that their source contains a component of recycled upper continental crust, we measured oxygen isotope compositions of olivine phenocrysts from these lavas. Correlations between δ¹⁸O of olivines (5.11‰–5.70‰) and ⁸⁷Sr/⁸⁶Sr and ²⁰⁷Pb/²⁰⁴Pb of whole rocks, as well as Ce/Pb and Nb/Th ratios of whole rocks, indicate that (1) measured δ¹⁸O are primary, mantle-derived values, and (2) the enriched mantle source of these lavas contains continental crust or its derivative sediments. The observed trend between δ¹⁸O and ⁸⁷Sr/⁸⁶Sr can be fit using either clastic marine sediment or continental crust values of δ¹⁸O, Sr concentration, and ⁸⁷Sr/⁸⁶Sr, but only those for clastic marine sediments are compatible with trace element modeling. We conclude that the enriched source for Samoan basalts was created by sedimentation of continent-derived material into a marine environment, followed by subduction and mixing with ambient mantle.