Extreme isotopic heterogeneity in Samoan clinopyroxenes constrains sediment recycling.

Abstract

Lavas erupted at hotspot volcanoes provide evidence of mantle heterogeneity. Samoan Island lavas with high ⁸⁷Sr/⁸⁶Sr (>0.706) typify a mantle source incorporating ancient subducted sediments. To further characterize this source, we target a single high ⁸⁷Sr/⁸⁶Sr lava from Savai'i Island, Samoa for detailed analyses of ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd isotopes and major and trace elements on individual magmatic clinopyroxenes. We show the clinopyroxenes exhibit a remarkable range of ⁸⁷Sr/⁸⁶Sr-including the highest observed in an oceanic hotspot lava-encompassing ~30% of the oceanic mantle's total variability. These new isotopic data, data from other Samoan lavas, and magma mixing calculations are consistent with clinopyroxene ⁸⁷Sr/⁸⁶Sr variability resulting from magma mixing between a high silica, high ⁸⁷Sr/⁸⁶Sr (up to 0.7316) magma, and a low silica, low ⁸⁷Sr/⁸⁶Sr magma. Results provide insight into the composition of magmas derived from a sediment-infiltrated mantle source and document the fate of sediment recycled into Earth's mantle.