A structural analysis of the San Antonio Formation, Rice Lake area, Manitoba

Abstract

The San Antonio formation is a feldspathic quartzite which has been folded into an anticline - syncline pair. The limb common to both folds is overturned to the south. Mesoscopic data indicate that the syncline plunges to the east; macroscopic and mesoscopic data indicate that the anticline plunges to the northwest. The anticline appears to be a product of flexural slip folding followed by slip folding along the foliation plane. A study of the microfabric reveals that the c-axes of the detrital quartz grains are preferentially orientated. Four maxima lie in two mutually perpendicular planes which contain "B1" and are 45* from "a" and "c". The maxima also lie on the surface of a cone, the axis of which is "B1". and the apical angle of which is 136*. This fabric is interpreted to be the preferential orientation of quartz along incipient S planes due to a compressive stress acting in the direction of the "a" geometric axis. The formation has been folded above an unconformity surface which may have acted as a decollement. The intrusion of a potassic rich granite north of the San Antonio formation appears to have caused the formation to be thrust southward. The thrusting was accompanied by folding in the San Antonio formation.