Evidence for extensional shear zones in the mantle, offshore Britain, and their implications for the extension of the continental lithosphere

Deep seismic profiles recorded in the seas around the British Isles have revealed bands of seismic reflections in the uppermost mantle. On the basis of their appearance, geophysical characteristics, and association with major crustal faults, these features are best interpreted as mantle shear zones. Furthermore, in the North Sea, the mantle reflectors appear to follow an extensional trend and, when interpreted as extensional shear zones, help explain the regional stratigraphy of the overlying basin. The crosscutting relationships between mantle reflections to the west of Scotland and a major strike-slip fault, the Great Glen Fault (GGF), suggest that the mantle structure postdates the GGF, and hence is probably related to subsequent extension. -from Author