Abstract

The ca. 2 Ga Kapuskasing zone, a 500-km-long belt of uplifted crust, cuts across the regional structural trend of the Archean Superior Province in Canada and disrupts the continuity of 2.45 Ga Matachewan dikes that form a major swarm in its vicinity. As expressed by positive gravity and magnetic anomalies, it appears to end about 100 km east of Lake Superior. Until now, the nature of this termination has remained obscure. Regional variations in paleomagnetic polarity and in the intensity of feldspar clouding caused by magnetite exsolution are two physical properties of the dike swarm that depend upon postemplacement erosion level. They show that the Kapuskasing zone, as a narrow, fault-bounded crustal uplift, continues, after sinistral offset, for a further 60 km to the southwest before terminating in a major cross fault. Dual magnetic polarity and variable levels of feldspar clouding are features found in many other Proterozoic dike swarms worldwide, and therefore, in principle, may be used to document other examples of craton response to tectonism.

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