Crustal structure across the Caledonides from the ‘WINCH’ seismic reflection profile: influences on the evolution of the Midland Valley of Scotland

ABSTRACTThe Western Isles–North Channel (‘WINCH’) deep seismic reflection profile runs through the North Channel across the extension of the Midland Valley into the Firth of Clyde.A variety of shallow Carboniferous and younger sedimentary basins dominates the upper crustal structure. The deep structure includes a reflective lower crust, bounded downwards by the Moho, and dipping ‘thrusts’. No margins to the Midland Valley are observed equivalent to the bounding faults on land. Thrusts below both the Highlands and the Southern Uplands have a variety of dip directions indicative of zig-zag crustal shortening of 100 km in the Highlands and 60 km in the Southern Uplands.The Moho varies only a little in depth, despite the gross crustal deformation in the Caledonides. Isostatic recovery of the Moho on unlocking of collided crustal blocks may explain the formation of some sedimentary basins.