PALEOGENE DYKE SWARM, NW WALES - EVIDENCE FOR CENOZOIC SINISTRAL FAULT MOVEMENT

The Berw and Aber-Dinlle Faults represent the brittle manifestation of a major lineament, the Menai Strait Fault System, which is known to h ave been active intermittently since late Precambrian times. Documenta tion of historical seismicity in this area provides information on the most recent activity along this structure, although there is a paucit y of field evidence to support conclusively Cenozoic or later movement s. This work documents data from three separate aeromagnetic datasets, combined with field relationships, which reveal a well-defined Cenozo ic dyke swarm traversing Anglesey and Snowdonia, showing clear sinistr al offset (up to 1.5 km) along the Berw Fault, the most northwesterly component of the Menai Strait Fault System. These data provide conclus ive evidence of Cenozoic (<65 Ma) strike-slip faulting in North Wales.