EVALUATING MODELS OF REVERSE-DRAG FOLDING

Rollover or reverse-drag folds are a common element of extended terrains and have been documented in association with both planar and listric faults. Widely applied kinematic models, however, require a listric fault profile to generate a hanging wall monocline. In contrast, mechanical models of normal fault deformation produce hanging wall folds in association with planar faults of finite down-dip extent. In natural examples where the fault geometry is unknown these two classes of models may yield statistically similar fits to the observed fold shape and yet imply radically different fault geometries and thus modes of crustal extension. An additional data set that may be used to further constrain the problem is the distribution of smaller scale structures such as joints and synthetic, antithetic, and bedding parallel faults. The kinematic and mechanical models yield different patterns of incremental strain and these may be compared to the distribution, and orientation of smaller structures. I apply this approach to the Lone Mountain Monocline of the western Grand Canyon and find that although both kinematic and mechanical models can fit the observed hanging wall fold and fault geometry; only the mechanical model predicts the observed footwall fold, the relationship between fold geometry and secondary faults and the occurrence of bedding-perpendicular extension.