Archean rocks form the eastern margin of the 1.1 Ga old Central North American rift along the eastern shore of Lake Superior and have been tilted westwards in response to rifting. Paleomagnetic and structural data from 2.6 Ga old Matachewan dykes suggest a westward crustal tilt of about 60°, which agrees well with dips recorded in nearby Keweenawan volcanics that rest directly on basement rocks. The Matachewan dyke swarm occurs throughout the east shore region of Lake Superior, whereas Keweenawan supracrustal sequences, which give a more precise estimate of tilt, are restricted to a few isolated shoreline patches. Estimates of crustal tilt can be obtained from the dykes on a regional basis, thus generating a more complete picture of basement deformation adjacent to a major intracratonic rift.

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