Deeply Recycled Origins of Mantle Heterogeneity at the Northern East Pacific Rise

Compositionally diverse lavas from the 8°20’ N seamount chain near the East Pacific Rise (EPR) record greater geochemical heterogeneity than observed along the entire northern EPR, including evidence for a 4-component mantle, and the first discovery of high-µ (high time-integrated ²³⁸ U/ ²⁰⁴ Pb) mantle source at the northern EPR. The amplitude of Pb, Sr, and Nd isotopic heterogeneity is on the scale of the Galapagos plume but in an area distal to a mantle plume. Our study combines isotopic and trace element compositions of near-EPR seamounts with recent mantle particle tracking models to identify deeply subducted origins for northern EPR mantle heterogeneity. We show that geochemical models (using He, Pb, Sr, Nd isotopes and trace elements) and geodynamic models (using time-dependent mantle flow simulations based on tomography) are self-consistent with tectonically recycled material feeding the northern EPR asthenosphere. These models provide a rare opportunity to assess geographic origins of mantle heterogeneity, tying the chemical and isotopic variability at the northern EPR to a paleo subduction zone at ~ 130 Ma, and reveal that one of the fastest spreading ridges on Earth samples deeply recycled components associated with whole mantle convection.