PALAEOMAGNETISM OF DIABASE DYKES OF THE CANADIAN SHIELD
Some areas of the Canadian Shield are profusely intruded by swarms of subparallel basaltic dykes. These typically have a diabasic texture and formerly were considered to be strictly the intrusive equivalents of tholeiitic flood basalt.About 650 oriented samples were collected from about 25 dyke swarms and preliminary palaeomagnetic data from six of them are presented here. The Mackenzie swarm has a K–Ar age of 1 295 million years, occurs throughout the western Canadian Shield, and is the most extensive swarm of basic dykes known anywhere in the world. The other swarms are the Molson dykes (1 445 m.y.) in northeastern Manitoba, the Marathon dykes (1 810 m.y.) just north of Lake Superior, the Sudbury dykes (1 285 m.y.) of southeastern Ontario, the Matachewan dykes (2 485 m.y.) of western Quebec and northeastern Ontario, and the Abitibi dykes (1 230 m.y.), which occur from Sault Ste. Marie, Ontario, to Lake Mistassini, Quebec.The palaeomagnetic virtual pole positions of six swarms were derived from the mean ...