Coupled trace element and isotope enrichment in the Cook-Austral-Samoa Islands, Southwest Pacific

Combined Pb-Sr-Nd isotope and trace element data are presented for eight islands within the Cook-Austral-Samoa island archipelago, southwest Pacific. These data reveal the presence of two geochemically distinct components within the OIB mantle. The Mangaia component represented by the islands of Mangaia and Tubuai has extremely radiogenic Pb isotopes but low 87Sr/ 86Sr . A Dupal component represented by Samoa has high 87Sr/ 86Sr , with low Pb ratios which are enriched in 207Pb and 208Pb. Nd isotope ratios of the Dupal component are slightly lower than for Mangaia. The Dupal isotope enrichment is coupled with high LIL/HFS element ratios relative to Mangaia. The Mangaia isotope enrichment is associated with low LIL/HFS element ratios comparable with or lower than MORB and indicates a time-integrated depletion in LIL elements in the source. However, inferred low ThU , and PbNb ratios indicate that Mangaia has been enriched in U but depleted in Pb relative to MORB. It is suggested that Mangaia could be derived from hydrothermally altered, subducted MORB. The Dupal component may include recycled subcontinental lithosphere.