Deep Structure, Evolution and Origin of the Icelandic Transverse Ridge

Abstract

The elevated Icelandic transverse ridge extends between the shelves of East Greenland and the Faeroe Islands. It is underlain by a three to four layered crust of oceanic affinity which is much thicker and more variable than normal oceanic crust but does not resemble normal continental crust. The thick crust accounts for the elevation relative to a normal oceanic cross section. The transverse ridge is terminated at its south-eastern end by an unusual type of margin between the Iceland-Faeroe Ridge and the Faeroe Block. The Mid-Atlantic Ridge crosses the otherwise aseismic transverse ridge at Iceland, beneath which the anomalous low density mantle appears to be more pronounced than beneath normal ocean ridge regions.

The transverse ridge probably originated in two successive stages by vigorous differentiation of crustal material from the hot underlying mantle during evolution of the North Atlantic. During stage 1 (about 60–42 My BP) the Iceland-Faeroe Ridge formed; the Iceland Block formed during stage 2 (about 42 My BP to present) which started with a major westward migration of the spreading centre. The Icelandic transverse ridge forms the abrupt culmination of a gradual northward shallowing of the Atlantic from the Azores towards Iceland, which can be interpreted in terms of raised asthenosphere temperature and slightly thinned lithosphere towards a high temperature focus beneath Iceland. The high upper mantle temperatures are tentatively attributed to a convective overturn 60–65 My BP rather than to a narrow plume rising from the lower mantle.