Variations of strength and localized deformation in cratons: The 1.9 Ga Kapuskasing uplift, Superior Province, Canada

The Kapuskasing Structural Zone was the site of local crustal thrusting and uplift within the Superior craton, presumably in response to stresses applied at the margin of the craton during the Paleoproterozoic ca. 1.9 Ga. We use the present-day heat flow data in the Superior Province to calculate the strength of the lithosphere and to show that the uplift took place in the weakest part of the craton. After eliminating heat flow data that were affected by the uplift and later events (Keweenawan rifting), we calculate the heat flow and the temperature field in the lithosphere at 1.9 Ga. We show that the Kapuskasing region was in the center of a “thermal anomaly” at this time. The strength of the lithosphere in this region may have been up to 2–3 orders of magnitude lower than in surrounding parts of the craton, depending on crustal heat source distribution. Uplift and the resulting erosion of the upper crust, as evidenced by geothermobarometry data from around Kapuskasing, led to a reduced crustal heat production compared to the average crust of the southern Superior Province. This reduced heat production resulted in low crustal temperatures and a strong lithosphere permitting the long term preservation of a crustal root.