A marine magnetic survey off southern Iceland

Total-intensity magnetic anomalies observed in a 1973 survey reflect contrasts in the structure of the southern Iceland shelf respectively west and east of 20°W. The western part, which is wider and more evenly sloping than the eastern part, has subdued magnetic relief indicating basement (basalt) depth of at least 400 m. On the eastern part of the shelf there occur pronounced edge anomalies, apparently due to a basement step of at least 1 km mean thickness and of mean width 3–4 km. The distance from the upper edge of this basement step to the bathymetric shelf edge increases from 5–8 km at 19°W to 12–14 km at 14°30W. The basement has alternating magnetic polarities. Linear magnetic anomalies are indistinct or absent in the surveyed region. It is speculated that the sharp basement step represents the trace of the maximum southerly extent of the eastern volcanic zone of Iceland.