Structural geology of the sickle and wasekwan groups, Mynarski Lakes, Manitoba

Abstract

Gneissic rocks within the Mynarski Lakes Area, northern Manitoba, belong to the Wasekwan and Sickle Groups of Precambrian age. Relict bedding So subparallels a regional foliation S1 which is defined by a strong parallel alignment of platy and prismatic minerals. Minor folding of S1 is common. Minor interference patterns encountered in outcrop suggest a complex structural history. Major folding of S1 and major interference patterns have been mapped within the area of this study. Five distinct deformational episodes have been recognized. The earliest, D1, resulted in formation of S1. The second deformational event D2 gave rise to tight concentric F2 folds of S1. The third deformational event D3 resulted in tight concentric F3 folds of S1. Major F3 fold hinges exhibit evidence of partial anatexis which is compatable with the low pressure, high temperature regional metamorphism of the sillimanite-cordierite-potassium feldspar, metamorphic subfacies of the Abukuma type facies series. The fourth deformational event D4 resulted in F4 tight, concentric, shallow plunging east-west trending folds. M4 metamorphism resulted in rotation and reorientation of M3 minerals without recognizable degradation. D4 appears to correspond to the Hudsonian orogeny in the area. A late episode of deformation D5 gave rise to faulting, associated F5 folding and a late retrogressive metamorphic event M5.