Folds and folding in the Beardmore–Geraldton fold belt

Abstract

The Beardmore–Geraldton fold belt forms a transitional crustal segment between the Quetico and Wabigoon subprovinces of the Canadian Shield.Bedding surfaces (So) and a bedding-plane schistosity (S1) were folded into asymmetrical to recumbent early folds. These folds were refolded by a later F2 folding episode. The F2 folds possess a penetrative axial-planar schistosity (S2) that is subvertical and generally strikes east–west. F2 hinge lines coincide closely with the axial direction of the early folds.The "structural facing direction (sensu Borradaile)" of F2 folds is either east or west. Folds with consistent facing directions are confined to distinct panels. Panels containing F2 folds with opposing facing directions are in sharp contact with each other. In several panels F2 folds face upward through sideways to downward.Modification of F2 buckle folds by homogeneous compressive strain components produced flattened flexure folds that closely approach folds of the similar fold model class.Further modification of fold shapes occurred in response to shear discontinuities that pervade the fold belt. Sheared F2 fold limbs commonly bind segments containing displaced F2 hinge zones of formerly adjacent folds. Zones of intense shearing show evidence of transposition of earlier fabric elements into the S2 schistosity. These zones of intense shear also form the boundaries of juxtaposed panels in which folds of variable orientation occur.The Beardmore–Geraldton fold belt is a terrain in which displacements along pervasive shear discontinuities of refolded folds and transposition of earlier fabric elements into the S2 schistosity have resulted in a pseudostratigraphy composed of disrupted and rotated segments of a pre-existing sequence of layered rocks.