A new Variscan deformation map of England and Wales

Abstract

Collections of bedding orientations from subareas of 550 km 2 are used to define bedding fabrics from the Variscan fold belt and foreland in England and Wales. The bedding fabrics, constructed from data taken from published geological maps (1 : 50,000 scale), are analysed in terms of the Scheidegger–Watson orientation tensor. The calculated eigenvalues of the orientation tensor define the average structural trends, including the best-fit fold axis, for each subarea, The eigenvectors of the tensor allow the original sedimentary fabrics to be distinguished from those modified by deformation. The progressive tectonic modification of these fabrics leads to the concept of fabric evolution paths, and the extent of the modification is expressed by a deformation parameter. Although it is emphasised that this parameter is not solely a function of finite strain magnitude, its variation is represented on a map which brings out different degrees of Variscan tectonic modification of bedding fabrics. This map delineates a Variscan bedding fabric front corresponding to the northern boundary of a zone of pervasive and strong deformation. In the foreland this new analysis allows the variation of Variscan trends to be mapped, and the significance of these trends to be quantified in terms of deformation magnitude.