Analyses of basement-involved fault-propagation folds in the Rocky Mountains suggest that hinges were defined early in fold evolution and the intervening fold limb (forelimb) was rotated and steepened as the structure amplified. A kinematic model is described that assumes fold hinges were fixed, the fault propagated through the forelimb, thickness changes occurred in the forelimb, and forelimb inclination increased progressively as slip increased on the underlying fault. The model is used to examine deformation in basement-involved folds in the Bighorn Mountains and Bighorn basin. Some of the assumptions for the kinematic model were relaxed when analyzing natural folds, to account for modifications in fold geometry resulting from the distribution of secondary structures.
Kinematic modeling techniques can be adapted by varying model parameters to simulate appropriate relative magnitudes of fault displacement and fault length for a specific stratigraphic section. Thus the models attempt to take account of mechanical characteristics that may show regional variations and control structural configurations.