Quetico Fault in the Superior Province of the southern Canadian Shield

Abstract

The Quetico fault is a major transcurrent fault in the southern Superior Province of the Canadian Shield. Along part of its length the fault forms the boundary between the Wabigoon subprovinces. Dextral motion on the fault by dextral microfaults and appropriately asymmetrical quartz c-axis petrofabrics. The fault comprises a zone of dynamically metamorphosed rocks - primarily mylonitic rocks with some cataclastic rocks and pseudotachylite. A transition from predominantly ductile deformation to brittle deformation occurred during the time the fault was active. The ductile deformation of quartz within the fault zone is the result of crystal-plastic processes, prism planes in the a-direction and slip on a-direction, accompanied by dynamic recovery and syntectonic recrystallization. Feldspar grains are commonly deformed in a brittle manner by fracture processes. Particulate flow appears to have made a significant contribution to deformation in the fault zone. The harmonic mean of deformed grain axial-ratios and strain determinations by the all object-object separations method indicate that flattening strain is predominant within the fault zone. The magnetic susceptibility anisotropy ellipsoid is also flat-shaped and coaxial with the strain ellipsoids. The characteristics of microfaults and folds within the fault zone indicate that flattening may have been accompanied by or followed by shearing. The harmonic mean of deformed quartz grain axial ratios yields a minimum strain estimate of 130% extension in X, 58% extension in Y, and 71% shortening in the 1 direction.