Extreme isotopic heterogeneity in Samoan clinopyroxenes constrains sediment recycling

Lavas erupted at hotspot volcanoes provide evidence of mantle heterogeneity. Samoan Island lavas with high 87 Sr/ 86 Sr (>0.706) typify a mantle source incorporating ancient subducted sediments. To further characterize this source, we target a single high 87 Sr/ 86 Sr lava from Savai’i Island, Samoa for detailed analyses of 87 Sr/ 86 Sr and 143 Nd/ 144 Nd isotopes and major and trace elements on individual magmatic clinopyroxenes. We show the clinopyroxenes exhibit a remarkable range of 87 Sr/ 86 Sr—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 87 Sr/ 86 Sr variability resulting from magma mixing between a high silica, high 87 Sr/ 86 Sr (up to 0.7316) magma, and a low silica, low 87 Sr/ 86 Sr 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. Subduction of oceanic crust and sediments contributes to heterogeneities in the mantle, which are sampled by mantle plumes. Here, the authors find that extreme isotopic heterogeneity in Samoan clinopyroxenes can help constrain the composition of mantle sources containing sediment recycled into the Earth’s mantle.