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

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 f swarms are considered to be the surface expression of lin ar intrusions emplaced in the lower to middle crust under theinfluence 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. Much of the modern work in the British Tertiary Volcanic Province (BTVP) has concentrated on the geochemistry and isotope geology of the wide variety of intrusive and extrusive rocks which compose the major centres of activity. However, since the centres were mapped in the first half o