PALEOMAGNETISM OF DYKES FROM THE GROUNDHOG RIVER BLOCK, NORTHERN ONTARIO - IMPLICATIONS FOR THE UPLIFT HISTORY OF THE KAPUSKASING STRUCTURAL ZONE

The groundhog River Block (GB) forms the central segment of the Kapuskasing Structural Zone a fault-bounded belt of Proterozoic crustal uplift in the southern Superior Province. Dykes adjacent to the GB carry a magnetization (D = 11-degrees, I = 26-degrees, alpha-95 = 27-degrees, N = 3) that is characteristic of 2.45 Ga Matachewan dykes. However, within the GB, dykes and high-grade gneissic host rocks carry a steep positive magnetization (D = 295-degrees, I = 83-degrees, alpha-95 = 12-degrees, N = 9) that also partially overprints the dykes immediately outside the GB. The boundaries between the contrasting paleomagnetic signatures coincide with boundary faults and changes in paleopressure that define the GB. The steep magnetization in the GB was acquired during uplift and cooling close to the time at about 1.95 Ga when a virtually antiparallel remanence of similar origin was being formed in the Chapleau Block, the southern segment of the Kapuskasing Structural Zone.