Structural Analysis along the Grenville Front near Sudbury, Ontario

Abstract

<p> Amphibolites and gneisses of the "Grenville province" and granitic rocks of the Chief Lake batholith near Sudbury show the effects of several phases of deformation. </p> <p> The first phase of deformation affected previously metamorphosed rocks of the "Grenville province" together with enclosed pegmatite sills, and formed congruous parasitic S- and Z-folds. The rocks were then subjected to faulting and local refolding. About 1, 750 m. y. ago, the Chief Lake batholith was intruded and truncated the previous folds. Finally, all the rocks were subjected to a simultaneous regional metamorphism and strong deformation. </p> <p> During this final deformation, all the previous linear structures were rotated to parallel the strongly-developed regional mineral lineations. The high-grade rocks of high amphibolite facies to the S. E. of the cataclastic zone flowed upwards from a greater depth than the rocks of greenschist facies to the N. E. of the cataclastic zone. The sharp increase in metamorphic grade occurs within the cataclastic zone which is about one mile wide. </p> <p> The final progressive deformation of the rocks is compared with the constant-volume deformation ellipsoid as initiated from the uniaxial prolate type through the constriction type to the plane- strain type; wherein the direction of maximum elongation plunges moderately to the S. S. E. and parallels the regional mineral lineations, the passive fold axes, the elongations of conical folds, and the original flow directions (shown by deformed mineral lineations) of slip folds; while the direction of maximum shortening generally plunges to the N. W. and is normal to the penetrative foliations and the active axial planes of slip folds. </p>