Geological inheritance and crystal dynamics of the northwest Scottish continental shelf

Abstract

Deep Seismic reflection profiles have been combined with conventional Seismic surveys across the northwest Scottish continental shelf to interpret basin development in the region. Post-Caledonian basins are built upon partially reactivated older structures which have strongly influenced their internal structure and stratigraphy. We show that the Minch Basin, along with several others, developed in the hangingwall of the partially reactivated Outer Isles Fault, a planar fault dipping at about 30° ESE that reaches nearly to the Moho. The internal structure of these hangingwall basins is compared with appropriate scaled analogue models to show that they have developed by passive hangingwall collapse above a footwall block that moved towards the WNW. This geometry is incorporated into a lithospheric dynamic model with northwest extension towards the Rockall Trough from a fixed lithosphere beneath the Scottish Highlands. This model requires non-linear lithosphere extension which is accommodated by movements on faults and block rotation in the upper crust, extension and thinning of the lower crust along a network of anastomosing ductile shears, extensional movement of the Flannan Fault in the upper mantle and horizontal displacement along the Moho beneath the Outer Hebrides. This dynamic model has wider application for other extensional regions.