Undersea Arctic Rocks Resemble Those in the Southern Hemisphere
08.05.2008 - Other
Scientists have found volcanic rocks under the Arctic Ocean having the same particular geochemical signature as rocks in the southern hemisphere. This discovery re-opens an underlying debate concerning the origin of such formations.
The Gakkel Ridge is Earth's most northerly undersea spreading ridge. Divided into an eastern and western volcanic zone by an unusually deep segment, the lavas on either side of the Gakkel Ridge have been shown to have different compositions. While the eastern lava closer to Siberia shows a typical northern hemisphere makeup, the western lava closer to Greenland displays a particular isotopic signature called the Dupal anomaly.
Up until now, the Dupal anomaly had only been found in the southern Indian and Atlantic Oceans and its origin had already sparked much debate among the scientific community. In the Arctic, though, scientists think they have nailed it. When Eurasia and Greenland began separating some 53 million years ago, the Gakkel Ridge rose as the spreading axis. Part of Eurasia's "keel" - a layer of mantle pasted under the rigid continent and containing specific elements also found in the continental crust - was peeled away from the continent and got mixed with the "normal" mantle rising at the Gakkel Ridge, which is normally deplete of these specific elements. This mixture caused the lava on the western side of the Gakkel Ridge to display the Dupal anomaly signature.
Although this discovery may not help determine the origin of the southern hemisphere Dupal anomaly, it "delineates an important process within Earth's system, where material associated with the continental lithospheric keel is transported to the deeper convecting mantle," as lead author Steven Goldstein, geochemist at Columbia University's Lamont Doherty Earth Observatory, puts it.
