Marine geophysical studies between northwest Scotland and the Faeroe plateau

Abstract

A marine geophysical survey of the northern Rockall Trough including the Banks to the north and northwest, the Wyville-Thomson Rise and the Hebridean continental shelf was carried out in 1970 and 1971,Gravity, magnetic and seismic reflection data indicates that the central Rockall Trough is underlain by about 5 km of sediment overlying a normal oceanic crust. The sedimentary thickness decreases to about 3 km and the crust becomes anomalously thick at the northern end of the Trough. Gravity and magnetic interpretation suggests that the Faeroe-Shetland channel is also underlain by anomalously thick oceanic crust. Gravity interpretation indicates that George Bligh, Bill Bailey's and Faeroe Bank are underlain by crust of continental thickness. The Wyville-Thomson Rise, which connects Faeroe Bank to the Scottish continental margin, is composed of two basement ridges of pre-Lower Oligocene age shrouded by sediments up to 1.5 km thick. The north easterly ridge is continuous from the Bank to the continental margin but the south westerly ridge terminates about 50 km from the margin. Magnetic and gravity evidence indicates that the ridges are composed of igneous material and that crustal thickening occurs beneath the ridges. An intrusive complex of unknown age lies beneath the southwest flank of the Rise. Gravity, magnetic and bathymetric interpretation indicates that the Hebridean continental shelf is underlain by Lewisian basement. Gravity and magnetic interpretation indicates that a NNE-SSW trending sedimentary basin about 1.5 km deep and with a partial covering of Tertiary lavas lies between Lewis and the Flannan Isles. Tertiary intrusive complexes, recognisable by their magnetic, gravitational and bathymetric effects, are present beneath St. Kilda, below the continental slope 75 km northwest of St. Kilda and beneath the shelf kO km north-northwest of the Butt of Lewis,