The structures of the Alpha Ridge, Arctic Ocean and Iceland-Faeroe Ridge, North Atlantic: Comparisons and implications for the evolution of the Canada Basin

Abstract

Based on organic fragments found in a sediment core retrieved from the eastern Alpha Ridge, it is concluded that 75 Ma ago this part of the ridge was an archipelago of forested islands which was formed above sea level about 95 Ma ago. Comparison of the Alpha Ridge with the Iceland-Faeroe Ridge (IFR) reveals remarkably similar morphological, geological and geophysical characteristics, except that the IFR crust is 7 km shallower and lacks the ridges and troughs of the Alpha Ridge. It is concluded that the Alpha Ridge is not a hotspot trace, but like the IFR was formed by funneling of volcanic material from a nearby hotspot into a spreading centre. It is suggested that the block-faulted nature of the Alpha Ridge is due to a collapse of the hot lithosphere, which at the time of formation was too weak to support the massive accumulation of plume material, whereas the lithosphere under the IFR was sufficiently strong to support the thinner crust. The Canada Basin may have evolved in two stages. In the Late Jurassic the southwestern Canada Basin opened. In the latter part of the Early Cretaceous, the whole Alaska-Siberian plate, including the southwestern Canada Basin and a continental Chukchi Borderland and Mendeleev Ridge, started to rotate away from the Canadian polar margin. It is postulated that the Icelandic hotspot, then located under Ellesmere Island, channeled plume material into the spreading axis, forming the Alpha Ridge. Channeling and spreading stopped after a rotation of 35°. Formation by seafloor spreading implies the youngest part of the ridge is near the centre, the oldest parts at either end. Indeed, the oldest sediment core of the Arctic Ocean was recovered from the Ellesmere end of the Alpha Ridge.