GEOPHYSICAL EVIDENCE FOR ULTRAWIDE DYKES OF THE LATE CARBONIFEROUS QUARTZ-DOLERITE SWARM OF NORTHERN BRITAIN

A compilation of the late Carboniferous quartz-dolerite dyke swarm of northern Britain has been made using existing geological maps, augment ed by new ground and airborne magnetic surveys. Aeromagnetic data in t he North Sea show that dyke anomalies can be traced eastwards on an ar cuate trend for up to 200 km from the UK coast, as far as the western margin of the Central Graben. Individual dykes, which are generally up to 30 m wide onshore, attain widths of well over 1 km offshore. These are at least as wide as any known dykes. The swarm is probably as ext ensive and voluminous as the well-known and better-exposed Palaeocene tholeiitic swarm of NW Britain.