Deformation in the core of a fold: Unraveling the kinematic evolution of tight, multilayer folds developed in the upper crust

Multilayer folding models provide a framework for evaluating fold kinematics, but have limited applicability for tight folds. A careful analysis of the tight Canyon Range (CR) syncline, a natural, multilayer fold (of alternating competent quartzite and incompetent argillite layers) formed in the elastico-frictional regime, yielded the following results. (1) Fracturing and cataclastic flow occurred at multiple scales. Variations in deformation style across scales are a function of matrix-controlled versus block-controlled cataclastic flow. (2) Competent and incompetent layers switched roles in controlling fold geometry between ∼40° and ∼60° limb dips; models predict this switch at 60°. (3) Parasitic folds formed during later stages of fold-tightening, while most models assume that they form during early stages of folding. (4) During fold-tightening, layer-parallel shortening structures were reoriented to accommodate vertical extension.We use multilayer folding models for initial first-order analysis of the CR syncline's kinematic history. Some of our data stray from model predictions. We use the location and timing of these variations to explain how/why the fold differs from anticipated results; this suggests critical details that may be overlooked and/or oversimplified in established folding models. Thus, kinematic details unraveled from the CR syncline improve our understanding of general multilayer fold models.