A Highly Depleted and Subduction‐Modified Mantle Beneath the Slow‐Spreading Mohns Ridge

Abstract

Abstract The Mohns Ridge is a very slow‐spreading ridge that, together with the Knipovich Ridge, marks the boundary between the North American and Eurasian plates in the Norwegian‐Greenland Sea. In this study, we report the major and trace element composition of spatially associated basalts and peridotites from a gabbro‐peridotite complex ∼20 km west of the Mohns Ridge rift flank. Formation of the ∼4–5 Myr crustal section involved accretion of normal mid‐ocean ridge basalts with Na‐content suggesting derivation from a depleted mantle source. This is consistent with the degree of partial melting estimated for clinopyroxene poor harzburgites using the Cr‐number of spinel (14%–18%) and rare earth element modeling of orthopyroxene (16%–24%) and reconstructed whole‐rock composition (14%–20%). If all the melting took place beneath the paleo‐Mohns Ridge, a crustal thickness of ∼7–8 km is expected, which is nearly double the observed thickness. Orthopyroxene trace elements are not consistent with typical fractional melting expected for mid‐ocean ridges but rather resemble that seen in supra‐subduction zone peridotites. The geochemistry of both the basalts and the peridotites suggests that a water‐rich slab flux in the past has influenced the mantle source. In turn, this caused hydrous melting which increased the depletion of the pyroxene components, leading to a highly depleted mantle that is now underlying much of the Arctic Mid‐Ocean Ridges and represents the source for the spreading related magmatism.

Keywords

• abyssal peridotite
• tectonic window
• Arctic Ocean
• chromium spinel
• partial melting
• melt‐rock interaction