A thin-skinned thrust model for Variscan Pembrokeshire, Wales

Abstract

The east and west coasts of Pembrokeshire (SW Wales) provide two sections through the Variscan fold and thrust belt. The evolution of these structures is interpreted in terms of a thin-skinned tectonic model. Balanced cross-sections are constructed for the high-level imbricate sequences, and these allow reasonably accurate estimates of shortening to be made. Basement control on structures developed in the Upper Carboniferous cover rocks is minimal, though some thrust ramp positions may be determined by the location of earlier normal faults. The thrust belt may be divided into two parts, according to the depth to the décollement horizon. In the north, imbricate fans developed from a shallow-level detachment (<1 km) which dips gently south. In the southern part, a deeper level of décollement and thicker sedimentary pile gave rise to large-amplitude folds. Shortening is heterogeneous, and both thrust periodicity and fold style are partly determined by rheology. Cumulative tectonic displacement increases to the west across Pembrokeshire, resulting in a net clockwise rotation of about 40°.