Structural zones of the Variscan fold belt in SW England, their location and development

Abstract

The D evonian and Carboniferous strata of SW England were deformed during the Variscan orogeny. Differing amounts of polyphase deformation imposed upon rocks of differing rheological character gave rise to a variety of attitudes and styles of folding. The present account attempts to outline the location and development of structural zones within which the attitudes of folds are constant. Dearman (1969a) suggested a zonal scheme based on the recognition of areas of upright primary folds passing southwards into inclined and recumbent folds on the north Cornish coast between Bude and Padstow. Continuity of this arrangement of structures eastwards to the western margins of Dartmoor can be demonstrated (Dearman 1971a). The zone of recumbent folding was extended, without subdivision, into south Cornwall. Simpson (1970) , recognising a zone of upright folding to the south of Brixham in south Devon, correlated this with the inclined folding in the Newquay area and thus subdivided the southern zone of recumbent folds. A line between Brixham and Newquay separates recumbent folding to the north from upright or inclined folding to the south, but this simple subdivision is unsatisfactory as recumbent first phase folds ( F 1 ) are common in the Mylor and Gramscatho Beds to the south of Perranporth ( Smith 1965 ). Neither zonal scheme, based solely on the attitude of fold axial planes, attempts to separate the north facing primary folds of south Cornwall and south Devon from the south facing primary folds of north Cornwall. In a discussion of the spatial relationships of the folding the following criteria