Structural geology of the Long Lake area, Manitoba

Abstract

At Long Lake Manitoba the Rice Lake greenstones have had a complex structural and metamorphic history. A period of isoclinal folding (D1) and greenschist facies metamorphism were the earliest events. They were followed by open cross folding (D2) accompanied by dynamic metamorphism and retrogression of biotite to chlorite. A period of minor kink folding (D3) was the last event. The development of folds during D1 is not well understood. During D2, folds were produced by passive slip parallel to a well developed axil plane foliation (S2) which strikes west and transects the axial surfaces of the early folds. The apparent direction to tectonic transport during D2 was parallel to mineral lineations (L2) and slickensides (L2') which pitch steeply to the east or west in the plane of S2. Volcanic fragments elongated in these directions and flattened in the plane of S2 are interpreted as possible evidence for near-vertical elongation and north-south shortening of the rock mass during D2. The last period of deformation (D3) resulted in a conjugate set of kink folds and a series of small concentric folds in the foliation (S2). These folds were probably produced by flexural slip on S2 parallel to a set of horizontal slickensides (L3).