Ancient refractory asthenosphere revealed by mantle re-melting at the Arctic Mid Atlantic Ridge

The upper mantle is a heterogeneous mixture of refractory and recycled crustal domains. portions, more fertile thus preferentially melted, dominate the composition basalts erupted on surface, whereas imprint melting counterparts difficult to discern from basalt chemistry. Contrasting radiogenic isotopic signatures mid-ocean ridge oceanic mantle, however, show that Hf isotope ratios may provide hints for source materials despite ubiquitous magma mixing during ascent stalling in crust. This property allow identifying contributions depleted unseen other systematics basalts. Here, we Mohns Knipovich ridges, two >500-km long oblique super-segments Arctic Atlantic, have distinctly high ratios, not mirrored by comparatively Nd low Sr Pb ratios. These compositions can be explained if highly asthenospheric melts beneath this section Mid Atlantic Ridge. We argue consists proportions ancient (>1 Ga), ultra-depleted previously drained enriched components before being re-melted its current location following recent ridge-jump, allowing identification arctic subridge mantle.