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.