The North Atlantic volcanic province has been attributed to continental rifting about 60 Myr ago over an Iceland plume head with a diameter of 1,000-2,000 km (refs 1, 2). But evidence from a few igneous centres has been used to infer that earlier plume activity occurred in this region. The three seamounts in the Rockall trough off the Atlantic coast of Scotland are among the few accessible remnants of such early plume activity. Here we present 40Ar-39Ar incremental-heating ages of samples from these seamounts, which show that volcanism began there in the late Cretaceous period (70 +/- 1 Myr ago), and then continued for the next 30 Myr in at least four discrete phases: 62, 52, 47 and 42 Myr ago. We relate this activity to pulsing of large masses (approximately 10(8) km3) of hot Iceland plume material on timescales of 5-10 Myr. This significantly extends the time span for Iceland plume activity both backwards and forwards in time, and provides a possible alternative to the 'plume head' models for the formation of continental flood basalts.