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Oxygen isotopes in Samoan lavas: Confirmation of continent recycling

¹ School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii 96822, USA
² California Institute of Technology, Pasadena, California 91225, USA
³ Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA

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 ¹⁸O 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 ¹⁸O 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 ¹⁸O and ⁸⁷Sr/⁸⁶Sr can be fit using either clastic marine sediment or continental crust values of ¹⁸O, 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.

Key Words: oxygen isotopes • Samoa • enriched mantle • EM2 • ocean island basalts