Geology of the Arctic Ridge System

The Arctic Ridge System consists of a series of ultraslow spreading ridges each with its own unique characteristics. All differ profoundly from the standard mid-ocean ridge geologic model. The Mohn’s-Knipovitch system is characterized by highly segmented volcanism and asymmetric seafloor spreading. To the north, the Molloy Deep is a pullapart basin floored by mantle peridotite that is the deepest point on the global mid-ocean ridge system at over 6000m. Proceeding northward, Lena Trough is a relatively young (~10 Ma) 350km long conjugate rift that has not yet undergone the transition from continental to oceanic rifting. Finally, the Gakkel Ridge, extending some 1800km across the Arctic Ocean, is the slowest spreading Mid-Ocean Ridge on Earth.

Mantle peridotites sampled from Arctic Ridges show an unexpected variety of geochemical signatures. The thick conductive lithospheric lid on these ultraslow spreading ridges results in crustal thicknesses that are less than half those seen at slow, intermediate and fast spreading ridges (Jokat, et al., 2003). Yet mantle peridotites sampled from arctic ridges show a range of compositions from relatively fertile (but not approaching pyrolite or similar compositions) to quite depleted. This variability may represent the remnants of primary mineralogical variability in the upwelling mantle, and not be due to melting beneath the Arctic ridges, being instead far more ancient (Liu, et al., 2008).

Pyroxenitic lithologies supportive of the “veined mantle” hypothesis are not seen directly along the Arctic Ridges. However, basalts erupted along the Arctic Ridges, particularly Gakkel Ridge, show a systematic pattern of increased incompatible trace element compositions that is similar to the southern hemisphere “DUPAL” anomaly (Muehe, et al., 1997; Goldstein et al, 2008). This suggests that the DUPAL anomaly may reflect the lower degree of partial melting along ultraslow spreading ridges.