An ancient, deep, and ultra-depleted mantle domain beneath the northern Atlantic Ocean

Abstract Mantle differentiation produces geochemically enriched crust and complementary depleted mantle residues. While crustal recycling over supercontinent cycles has shaped a first-order east-west mantle compositional dichotomy between an enriched African mantle domain and a depleted Pacific mantle domain, the nature, distribution and origin of depleted mantle heterogeneities remain poorly known. Here we report the presence of an ultra-depleted mantle domain beneath the northern Atlantic Ocean, characterized by highly depleted elemental compositions and radiogenic Hf isotopes. We develop a statistical mantle model to reconstruct distinct mantle depletion histories, which can also explain the Hf-isotope discrepancy between oceanic basalts and peridotites. Model results indicate that the ultra-depleted mantle (UDM) domain records ancient high-degree melt extraction at depths greater than those of normal mid-ocean ridge melting. In contrast, a depleted Pacific mantle domain reflects a progressive melt extraction that mostly occurred at shallow depths, compatible with those of mid-ocean-ridges. We propose that distinct melt-depletion histories contribute to mantle’s compositional structure, in which the UDM domain beneath the northern Atlantic Ocean may represent residues of ancient mantle plumes that have been preserved in the lower mantle.