Fabrics and Deformation of Archean Metasedimentary Rocks, Ross Lake – Gordon Lake Area, Slave Province, Northwest Territories

• Published in: Canadian Journal of Earth Sciences
• Main Author: Fyson, W. K.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1975
• Subjects: Northwest Territories
• Online Access: http://dx.doi.org/10.1139/e75-067; http://www.nrcresearchpress.com/doi/pdf/10.1139/e75-067

Metagreywackes, which lie stratigraphically above metavolcanics fringing a granitic complex (part basement), exhibit late Archean multiphase fold structures. F 1 folds are large linear depressions and anticlinal culminations trending partly concordant with margins of the granitic complex. Open to isoclinal F 2 folds vary and curve in trend. Though usually near upright, some F 2 folds are overturned away from the complex and others towards F 1 depressions. F 3 folds are small-scale structures not present in most outcrops, but throughout a large region they are accompanied by a steep S 3 axial-plane schistosity striking NW to N.Original orientations of an S 2 schistosity, axial planar to F 2 folds, are preserved as inclusion trails in biotite porphyroblasts. Angular deflections from the trails show that regional horizontal flattening across the S 3 schistosity formed the F 3 folds and tightened curved trends of F 2 folds. Estimates of strain from the fabrics indicate no increase near the complex.As for folds in other Archean terrains, F 1 and F 2 folds could have developed mainly as gravity structures during diapiric uprise of a granitic basement. In contrast, the F 3 structures may reflect horizontal movements of early crustal plates.