In situ stress compared to structures in Lac du Bonnet Batholith, Manitoba, Canada

Abstract

Structural fabrics in a late Archean/early Proterozoic granite batholith at Lac du Bonnet, Manitoba, Canada, have been used to develop the temporal sequence of paleostress axis orientations. Orientations of the in situ stress field have been measured, both at surface and below surface at Atomic Energy of Canada Ltd.'s Underground Research Laboratory, through the techniques of borehole hydraulic fracturing, overcoring, and shaft wall convergence, and through quarry data and surface pop-ups. The fabric, interpreted paleostress and in situ stress directions are compared with each other and with regional stress orientations suggested by other authors for the western Superior Province. North, and NNE to NE trends for in situ maximum compressive stresses measured above the 250-m depth, possibly contain a large component of remanent stress. In situ stresses with SE to SSE trends are common near NE-striking thrust faults below the 250-m depth. This could be a Proterozoic remanent stress recovery, or it could be fabric-controlled. Neither NE- nor SE-trending in situ measurements wholly represent that of the present-day plate-induced active tectonic stress.