Deep seismic reflection survey across the Variscan Front of southern England

Abstract

In 1979, the Institute of Geological Sciences commissioned two lines of seismic reflection profile, a technique which has proved successful1 for studying crystalline basement. The survey was sited to cross the concealed Variscan Front in southern England, with recording time extended to 12 s two-way time (TWT). Similar profiles in adjacent parts of Europe have suggested that the Variscan Front is characterized by major thrust zones extending to considerable depths2,3. Our profiles, reported here, show good primary reflections to 6 s TWT and give new detail on the nature of Variscan deformation in southern England. Zones of differing reflection character are evident; a northern zone of low northerly apparent dips, a central zone of poor reflector quality, and a southern zone of steeper dips to the SSE. The southern zone is presumed to represent deformed Variscan basement, including several minor thrust planes and a proposed major thrust zone, analogous to similar structures in Europe. Impersistent reflections between 9 and 10 s TWT could possibly relate to the Moho.