20. Superposed Folds

Superposed folds are complex folds formed due to superposition of an early-developed fold set by some later fold set(s). The resultant fold geometry is said to show a fold interference pattern. Superposed folds may form during a single deformation event or during different deformation events of a single orogeny. These folds commonly occur in most orogenic belts. The classical grouping of superposed folds is in two dimensions. However, some later workers have also considered three-dimensional grouping of superposed folds. Although our understanding of superposed folding is broadly field based, experimental studies of both single-layer and multilayer folds have thrown significant light on their mode of formation. Reconstruction of three-dimensional shapes of the superposed folds, and thus outlining the stages of evolution of the superposed folds, is sometimes difficult. However, the study of the reorientation of lineations and cleavages or the relations between folds and cleavage or lineation can help in distinguishing the earlier and later generations of folds. Recently, the concepts of progressive deformation and deformation phase are being considered in the context of fold superposition.