Structural variation across the northern margin of the Variscides in NW Europe

Summary Four areas which cross the northern margin of the Variscan fold belt are examined and models of their structural evolution, from basin development to folding etc., are compared. Foreland Britain is characterized by heterogeneous deformation localized in basins, whose development accompanied E-W dextral shear. The Munster basin in Ireland contains steep folds and cleavage. A variety of minor structures indicates an important dextral shear component to the deformation, and basin inversion by transpression is proposed. SW England is dominated by thrust tectonics, including the obduction of the Lizard ophiolite. Deformation was preceded by south to north migration of basin development. Brittany is characterized by major dextral shear zones delimiting areas of variable ductile strain. The structural geometry and history of these areas is interpreted in terms of regional dextral transpression. The common transport direction is to the NNW or NW and oblique to the belt. Variable amounts of thrusting and dextral shear produced the different structural patterns. A case is made for an essentially ‘thick-skinned’ style of heterogeneous deformation produced in a dextral, oblique collision orogen, which involved microplates and a small back-arc basin.