The early Tertiary stress regime in NW Britain: evidence from the patterns of volcanic activity

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Abstract
Summary: Major dyke swarms emplaced throughout the Palaeocene volcanic episode in the British Tertiary Volcanic Province indicate NE-SW extension occurred perpendicular to the evolving NE Atlantic continental margin. Sigmoidal N-S orientated secondary swarms cutting Lewisian basement structures indicate a possible dextral shear component within the regional NE-SW extensional stress field, rather than a structural control on dyke emplacement. Both groups of swarms are considered to be the surface expression of linear intrusions emplaced in the lower to middle crust under the influence of the regional extension. Patterns of faulting within the province are consistent with the stresses recorded by the dyke swarms, indicating the stress field persisted into the Eocene during which a change to NW-SE extension occurred.