North Atlantic Oceanic Topography and Lateral Variations in the Upper Mantle

A thermal model of sea-floor spreading applied to the northern Mid-Atlantic Ridge at several latitudes suggests that lateral variations of upper mantle structure in both the asthenosphere and the lithosphere may exist beneath the ocean, extending from Iceland to the Azores. The variation of ocean ridge cross-sectional area and the general shallowing of the sea towards the north which occur in the Atlantic may be explained by sea-floor spreading taking place above an asthenosphere whose temperature at a given depth increases northwards, with Iceland perhaps the focus of the thermal field. The relationships between asthenospheric temperatures, lithospheric thicknesses and ocean ridge dimensions derived here should be applicable to studies of other ridges.