A comparative 40Ar/39Ar study of the Kapuskasing structural zone and the Wawa gneiss terrane: thermal and tectonic implications

Abstract

40Ar/39Ar studies were performed on rocks from two traverses within the southern Superior Province of the Canadian Shield: the Racine traverse across the Wawa gneiss terrane and the Shawmere traverse in the highest grade rocks of the Kapuskasing structural zone (KSZ). Evidence of differential uplift between the two regions was obtained from the hornblende samples analysed. The results suggest that the Wawa gneiss terrane cooled below the hornblende closure temperature about 2570 Ma ago, whereas the KSZ region remained at depth, above the hornblende closure temperature, until about 2450 Ma ago. The Racine biotite samples indicate earlier cooling for the northern region in respect to the southern region within the Wawa gneiss terrane. This would imply tilting in a roughly north-south direction about 2300 Ma ago. Low ages (ca. 1100 Ma) obtained in low-temperature fractions of the microcline samples record the intrusion of the alkaline complexes.