Basement fractures in North Wales: their recognition and control on Caledonian deformation

Abstract

AbstractA detailed survey of the patterns of regional deformation in North Wales has revealed the presence of several discrete, linear zones of anomalous deformation. These zones are distinguished by atypical finite strain values, intense tight to isoclinal folding, non-axial planar cleavages and high metamorphic gradients. A history of prolonged tectonic activity along these zones is indicated by their influence on sedimentation and volcanism. It is proposed that these zones reflect the deformation of the Lower Palaeozoic cover above pre-existing basement fractures. These basement fractures form a framework which divides North Wales into a series of blocks and sub-blocks. The end-Caledonian deformation is explained by a transpression model dominated by SE-directed shear with minor components of strike-slip localized in these zones. The application of this model to other parts of the Welsh Basin is briefly considered.