RESTORATION AND BALANCING OF A CROSS SECTION OF THE MT. CRANDELL DUPLEX, WATERTON NATIONAL PARK, CANADA

Cross-section balancing provides a useful tool for checking the potential viability of structural interpretations through complexly deformed terranes. Balanced cross sections contain structures that are similar to those observed in outcrop or on seismic profiles in the area, that can be restored to a realistic pre-deformational configuration of faults and undeformed strata where areas are preserved between the deformed and restored states, and whose development from the undeformed state can be described in a kinematically reasonable sequence. Quick-look inspection of cross sections greatly facilitates the balancing process by comparing corresponding hanging wall and footwall features (particularly focusing on ramps and flats) to identify areas in a cross section that may contain balancing issues.

The well-known Boyer and Elliott (1982) cross section through the Mt. Crandell duplex in Waterton National Park in Alberta, Canada and its accompanying restoration have long served as a classic example of a balanced cross section. We carefully examined the section and its restoration using quick-look techniques, and noted several structures that had substantially changed their shape between the deformed and restored states, had ramp-flat mismatches between the hanging wall and footwall, and/or had significant area changes between the deformed and restored states. Using cross-section restoration software, we not only quantified differences between their deformed-state and restored-state cross sections, but we also rigorously restored their original section. Specifically, we identified differences in areas between their deformed and restored horses that ranged from 1.939% to 185.014%, and noted two horses missing in the restoration. In addition, the computerized restoration revealed multiple issues with ramp-flat geometries that produced substantial gaps and overlaps not reflected in the original restoration. Based on careful examination of these problematic areas, we refined the Boyer and Elliott (1982) deformed-state cross section to help address these issues. Restoration of our modified cross section suggests that it balances better than the original version.