Seismic reflection data and the internal structure of the Lake District batholith, Cumbria, northern England

Abstract

SUMMARY Seismic reflection data across the western margin of the Lake District batholith reveal reflector-poor and reflector-rich areas within components of the intrusion. Synthetic seismograms generated from a series of velocity models have been used to interpret a representative panel of a seismic reflection profile across the western boundary of the batholith. Results indicate that the reflections bounding large, wedge-like reflector-rich zones may be associated with granite/country rock acoustic impedance boundaries. The reflector-rich zones are interpreted as bodies of country rock intruded by the granite and the reflection-poor areas as laccolithic granitic components of the batholith. Reflector-rich areas within the main body of the Lake District batholith may arise from either areas of included country rock, sills or fracture zones within the granite. The areal extent of the wedge-like zones of reflections suggests the intrusion hereabouts comprises a series of laccolithic bodies. It is interpreted that the subsurface western margin of the intrusion has a jagged, ‘cedar-tree’ profile, the intrusive envelope to which is steeper than previous gravity models imply for a ‘simple’ batholith margin. Such a configuration is compatible with observed gravity data.