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.