Implications of meso-structures for deformational history of the Moose Mountain structure, Canadian Rocky Mountain foothills

We use small-scale structures (meso-structures) to investigate strain and to interpret the deformation history of the Moose Mountain structure in the southern Canadian Rocky Mountains. Small-scale structures measured at seven sites encompass 440 measurements of fault planes with striations, veins and fold axes. Kinematic analysis suggests that these meso-structures record three different shortening directions that changed during the evolution of the Moose Mountain structure from NE–SW–ENE–WSW, to E–W and subsequently to NNE–SSW. NE–SW–ENE–WSW shortening is compatible with the large-scale geometry of the Moose Mountain structure and with thrust-fault orientation in the study region, whereas the relationship with E–W and NNE–SSW shortening is less obvious. Small-scale reverse faults and part of the veins are interpreted as forming during early deformation in association with the development of the macro-scale thrust faults of the Rocky Mountains, whereas the mesoscopic strike-slip faults, veins and micro-folds developed later. A relatively large number of the strike-slip faults and veins are interpreted to have been generated by reactivation of pre-existing structures. This study demonstrates again that small-scale structures can discriminate modifications in regional strain directions and identify moderate episodes of deformation within deformed terrains such as the Foothills thrust-belt.