An evaluation of models for the kinematic evolution of thrust and fold belts: structural analysis of a transverse fault zone in the Front Ranges of the Canadian Rockies north of Banff, Alberta

The prevailing 'piggyback' conceptual model fur the kinematics of 'thin-ski nned' thrust and fold belts maintains that the main faults develop sequenti ally from the hinterland to the foreland, and from the top to the bottom of the accretionary wedge. Moreover, it presumes that when younger thrust fau lts originate, overlying older thrust faults become inactive and are carrie d forward passively. This appears to contradict the prevailing mechanical m odel for the evolution of 'thin-skinned' thrust and fold belts, the critica l Coulomb wedge model, which requires that lateral growth of the wedge must be accompanied by vertical thickening of the wedge. Crosscutting relations hips along a transverse fault zone in the Front Ranges of the Canadian Rock ies north of Banff Alberta, and patterns of overprinting of thrust-related folding on pre-existing thrust sheets, demonstrate substantial overlap in t he times of displacement on four major thrust faults in this part of the Fr ont Ranges. The presumption that displacement on one major thrust fault end s when displacement on a younger underlying thrust begins is a fallacy. The re is no contradiction between the 'piggyback' conceptual kinematic model a nd the critical Coulomb wedge mechanical model for the evolution of 'thin-s kinned' foreland thrust and fold belts. The main faults do originate sequen tially from the hinterland to the foreland, and from the top to the bottom of the evolving wedge; but displacement occurs simultaneously on several ma jor faults. (C) 2001 Elsevier Science Ltd. All rights reserved.