Mechanics of the giant radiating Mackenzie dyke swarm: A paleostress field modeling

The 1.27 Ga Mackenzie dyke swarm of the Canadian Shield is a giant radiating dyke swarm that gradually swings in orientation from N-S in the focal area to NW-SE trends in peripheral areas. In this paper, we propose a new model (the "Plug'' model) that accounts for the paleostress contribution to the mechanism of emplacement for the Mackenzie dyke swarm in the Canadian Shield. The 1.27 Ga stress field on the Canadian Shield calculated by the "Plug'' model explains the radiating nature of the Mackenzie dyke swarm around the Coppermine River lava field by local stress concentrations. The parallel nature of the dyke swarm at distance (more than 1000 km) from the focal source can be explained by the existence of a regional tectonic stress field created by ridge push acting on the southeast margin of the Canadian Shield from the Grenville Ocean. The thin elastic plate and two-dimensional cross-section modeling suggest that the interaction between stresses from a mantle upwelling and the Grenville Ocean spreading play an important role in the intrusion mechanism of the Mackenzie dyke swarm. The change in dyke orientation from N-S trending to NW-SE trending is caused by coupling between resistance from the focal area (Plug area) and a Grenville Ocean ridge push.