Abstract The Rheic Ocean is a persistent feature of Paleozoic palaeogeographies whose closure contributed to the development of the Variscan Orogen and the formation of Pangaea. Geological and geophysical data indicate repeated episodes of Paleozoic rifting and plate convergence around SW England and the adjacent offshore areas. SW England occupied a lower plate position during the Devonian–Carboniferous, on the northern passive margin of the short-lived Rhenohercynian Ocean that had formed near a recently closed segment of the Rheic Ocean. Variscan plate convergence resulted in the development of the composite southwards-dipping Rheic–Rhenohercynian suture zone by the latest Devonian and inversion of the lower plate basins during the Carboniferous. Early Permian NNW–SSE extensional reactivation of this suture zone controlled the development of the Western Approaches basins in its hanging wall and provides an excellent example of Wilson cycle structural inheritance. The onshore expression of this episode includes shear zones and detachment faults consistent with top-to-the-SSE extensional reactivation of Variscan thrust faults. There is a progression to higher-angle brittle extensional faults that cut out earlier structures. Exhumation of the lower plate was accompanied by Early Permian mantle and concomitant crustal partial melting, the construction of the Cornubian Batholith and W–Sn–Cu fracture-hosted mineralization.

Abstract The upper Palaeozoic Orogenic Province of SW England is a part of a belt of Devonian and Carboniferous basins that extended from Devon and Cornwall through to Germany, some 800 km to the east. Their complex sequence of basin development and phases of deformation, described in this chapter cumulatively comprise the Variscan Orogeny in this region. Synchronously with the Devonian events within the Variscan Orogen, the mainly fluvial facies of the Old Red Sandstone filled basins in the Avalonian continent north of the Variscan front (Chapter 6). During the succeeding Carboniferous, basins within the continent were mainly extensional in origin, until a period in the late Carboniferous when many basement faults were inverted (Chapter 7) resulting in uplift of the basin fill, that initiated a new palaeogeography at the start of the Permian. The South Wales Basin represents a transitional zone between the mobile Variscan belt and the continent to the north. This transitional position is reflected in the Devonian by the interdigitationof the Old Red Sandstone facies and marine sediments at the northern margins of the Variscan basins (Chapter 6). Throughout the Dinantian and Namurian the succession within the South Wales basin had much in common with successions in basins within the continent to the north (Chapter 7). It was not until the Silesian that Variscan deformation affected basin development and caused its deformation (see this chapter).