page_title: Mackenzie Large Igneous Province
section_title: Extensional forces
hierarchical_section_title: Mackenzie Large Igneous Province / Geology / Extensional forces
caption_attribution_description: English: Tectonic and magmatic feature associated with the Mackenzie Large Igneous Province. Red star shows the initial Mackenzie plume zone relative to the lithosphere; partial black circle is the estimate of the zone of plume influence on stress-field orientation; dark lines are dikes of the Mackenzie swarm; CRB indicates the Coppermine River basalts; M indicates the Muskox intrusion.
context_page_description: The Mackenzie Large Igneous Province is a major Mesoproterozoic large igneous province of the southwestern, western and northwestern Canadian Shield in Canada. It consists of a group of related igneous rocks that were formed during a massive igneous event starting about 1,270 million years ago. The large igneous province extends from the Arctic in Nunavut to near the Great Lakes in Northwestern Ontario where it meets with the smaller Matachewan dike swarm. Included in the Mackenzie Large Igneous Province are the large Muskox layered intrusion, the Coppermine River flood basalt sequence and the massive northwesterly trending Mackenzie dike swarm.
  As a large igneous province, it is an extremely large area of related igneous rocks that were emplaced over an extremely short geological time span. The igneous rocks comprising the Mackenzie Large Igneous Province originated from processes not associated with normal plate tectonics and seafloor spreading. It is one of the several large igneous provinces scattered throughout the Canadian landscape, which can be thousands of kilometres in volume and area.
context_section_description: At the beginning of the Mackenzie magmatic event, the Mackenzie hotspot collided with lithosphere that was already in an extensional regime that allowed rifting to occur. Passive rifting has been interpreted as the mechanism that produced the opening of the former Poseidon Ocean, the geometry of which would have been partly controlled by dike swarm geometry. Fahrig (1987) proposed that the Mackenzie plume impact resulted in the emplacement of a triple junction that had a large mafic dike swarm on every rift arm. Two of the first arms formed the Poseidon Ocean basin and the third arm failed thus forming an aulacogen. This tectonic setting suggestion can be comparable with the early volcano-tectonic evolution of the Yellowstone hotspot, which developed two arms instead of three, followed by failure of both arms. At the Mackenzie hotspot, rifting is considered to have been passive and to have taken place in the crust above the hotspot that should have been weakened by the Mackenzie plume. Crustal uplift may have also provided stresses contributing to rifting.
  A slightly younger but possibly related geologic feature is the 2,000 km (1,200 mi) long Midcontinent Rift System adjacent to the southern end of the Mackenzie Large Igneous Province. The Lake Superior portion of the Midcontinent Rift System is bounded on the south by pre-existing continental faults that had substantial right-lateral movement before the formation of the Midcontinent Rift System. This period of rifting was a large event for copper mineralization, and the rifting event later deceased when the Grenville orogeny collision occurred.
caption: Tectonic and magmatic features associated with the Mackenzie Large Igneous Province. Red star shows the initial Mackenzie plume zone relative to the lithosphere; partial black circle is the estimate of the zone of plume influence on stress-field orientation; dark lines are dikes of the Mackenzie swarm; CRB indicates the Coppermine River basalts; M indicates the Muskox intrusion.
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