Patterns of late Caledonian intrusive activity in eastern and northern England from geophysics, radiometric dating and basement geology

Abstract

SUMMARY Consideration of the petrological relationships and the physical properties of the concealed igneous rocks in eastern England, together with isotopic dating results and seismic refraction data, reveals a migrating three-phase sequence of Caledonian igneous activity culminating in a period of granitic intrusion during early Devonian times in the Wash and north Norfolk areas. Comparisons between the geophysical characteristics of these eastern England features and those of other known Caledonian granitic intrusions confirms their interpretation as granite batholiths. Since eastern England was isolated from the complex tectonic activity of the Caledonian orogeny, it is only in the Lake District that a similar sequence of intrusion can be recognised, with gradual increase in acidity of the intrusions during the Lower Palaeozoic. The Pennine and Lake District granites are linked to the eastern England batholith by a north-west to south-east trending belt of magnetic basement. On the margins of this belt are located two further, but as yet unsampled, features with which are associated large negative gravity anomalies with characteristics similar to those of the granites of northern England and of the postulated granites in eastern England, which lie more to the centre of the magnetic belt. Late Caledonian acid intrusions may therefore be more widespread than previously thought.