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 depths^2,3. 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.