The Gakkel ridge, which extends under the Arctic ice cap for ∼1,800 km, is the slowest spreading ocean ridge on Earth. Its spreading created the Eurasian basin, which is isolated from the rest of the oceanic mantle by North America, Eurasia and the Lomonosov ridge. The Gakkel ridge thus provides unique opportunities to investigate the composition of the sub-Arctic mantle and mantle heterogeneity and melting at the lower limits of seafloor spreading. The first results of the 2001 Arctic Mid-Ocean Ridge Expedition (ref. 1) divided the Gakkel ridge into three tectonic segments, composed of robust western and eastern volcanic zones separated by a ‘sparsely magmatic zone’. On the basis of Sr–Nd–Pb isotope ratios and trace elements in basalts from the spreading axis, we show that the sparsely magmatic zone contains an abrupt mantle compositional boundary. Basalts to the west of the boundary display affinities to the Southern Hemisphere ‘Dupal’ isotopic province2, whereas those to the east—closest to the Eurasian continent and where the spreading rate is slowest—display affinities to ‘Northern Hemisphere’ ridges. The western zone is the only known spreading ridge outside the Southern Hemisphere that samples a significant upper-mantle region with Dupal-like characteristics. Although the cause of Dupal mantle has been long debated, we show that the source of this signature beneath the western Gakkel ridge was subcontinental lithospheric mantle that delaminated and became integrated into the convecting Arctic asthenosphere. This occurred as North Atlantic mantle propagated north into the Arctic during the separation of Svalbard and Greenland.
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We thank A. le Roex for comments that helped to improve this paper. This work was supported by the US National Science Foundation. G.S. was supported partly by a Paul and Daisy Soros Fellowship for New Americans.
The geochemical data reported here are available in the Petrological Database of the Ocean Floor (http://www.petdb.org).
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Goldstein, S., Soffer, G., Langmuir, C. et al. Origin of a ‘Southern Hemisphere’ geochemical signature in the Arctic upper mantle. Nature 453, 89–93 (2008). https://doi.org/10.1038/nature06919
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