The tectonic significance of some basic dyke swarms in the Canadian Superior Province with special reference to the geochemistry and paleomagnetism of the Mistassini swarm, Quebec, Canada

Abstract

The Mistassini dykes extend northwest from the Mistassini embayment and comprise both tholeiitic and komatiitic suites. They are probably > 2000 Ma old and yield two major paleomagnetic components. One of these, with a pole at 131°W, 13°S, is thought to be an overprint related to the Elsonian Disturbance 1400–1500 Ma ago. A very steeply down (and reversed) component may be primary and has a pole at 080°W, 50°N.These spacial, chemical, and age relationships between the Mistassini, Molson, Marathon, and Payne River dyke swarms and the Aphebian supracrustal fold belts on the perimeter of the Superior Province suggest a genetic relationship between the dyke swarms and the fold belts. The supracrustal belts are evidence of the opening and closing of oceans, and the dyke swarms are evidence of early-stage failed arms related to these openings. More rarely (for example, the Payne River dykes), early-stage dyke swarms are developed and preserved parallel to the edges of newly developed spreading plate boundaries. Presumably if a spreading episode stops, the dykes themselves may remain as the only evidence of that event. Probably all the world's great continental dyke swarms have the above-described tectonic setting, and the number and extent of dyke swarms during a geological epoch may be a measure of the number and vigour of spreading events.