The deformational history of the south central portion of the Munro Lake greenstone belt, northern Manitoba

Abstract

The rocks of the Gods Lake Subgroup and the overlying Knee Lake Subgroup have undergone a complex structural history in the south-central portion of the Munro Lake greenstone belt of northern Manitoba. During D1 a strong tectonic foliation (s1) was developed by recrystallization, clasts (dc1) were flattened parallel to the s1 foliation plane, and minor shear folds (f1') were developed in bedding (s0) with the s1 foliation axial planar to them. The deformation during D1 may have been the result of pure shear accompanied by recrystallization and followed by passive slip (simple shear) or it may have been the result of simple shear accompanied by recrystallization and a minor component of flattening (pure shear). Flexural slip folding of bedding (s0) and foliation (s1) occurred during the second period of deformation. Foliation was the active surface in this deformation. At least two orders of flexural folds (f2', f2") are associated with D2. Deformed clasts (l2) and mullions (m2) are are second event b-lineations and plunge parallel to the f2' fold axes. The third period of deformation resulted in gentle folding about an axis approxiamately perpendicular to the earlier axial planes. This caused a slight reorientation of D2 linear structural elements and folding of bedding and foliation where they are subhorizontal. The fourth period of deformation was a period of minor faulting which displaces the earlier structural elements. The mode of origin of the Munro Lake syncline is open to speculation. It may have formed during the first or second period of deformation documented within the study area.