Abstract

The Grenville Front Tectonic Zone extends as much as 30 km into the Grenville Province of Ontario, but reaches only a few kilometres into the Superior and Southern Provinces. For a distance of >75 km, this tectonic zone passes through a large granitic body, the Ingall Lake Batholith. Here the Superior portion of the zone is characterized by numerous north to northeast trending faults which cut the Grenville Front Boundary Fault. One of these younger structures, the Kettle Lake Fault, is exposed on Highway 11 about 1 km north of the Grenville Front Boundary Fault. Its mylonites are generally derived from feldspar-porphyritic trondhjemite, and contain numerous folded dykes of pink aplite.The folds plot into J. G. Ramsay's class 1C field, and represent flattened buckles. Using Ramsay's methods, C/B (flattening) and C (buckling) were estimated for the preserved parts of seven minor folds. The remaining components of overall strain were calculated on the basis of k-values obtained for the mylonitic trondhjemite adjacent to the buckles. Susceptibility anisotropy determinations provided an objective but minimal measure of k. The dilatational part of the deformation was ignored by putting ABC = 1. Thus for B (buckling) we found that B3B2C(1 −(1/k)) − 1/k = 0. This cubic equation has one real root B and two conjugate imaginary roots. Similarly for the flattening phase, A/B = 1 − k(1 − (B/C). Total strain components were obtained by superimposing the flattening strain on the buckling strain. Maximum values of C range from 0.081 to 0.395 depending on the severity of mylonitization.

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