Folds and Folding

Abstract

Some of the basic information related to development of folds are provided, e.g. why, where, and how do they develop. Fold propagation and fold geometries resulting from interference of simultaneously developing folds are described in two and three dimensions along with causes of noncylindricity. Variations of fold geometry along the hinge line, and with depth along the axial surface are shown by natural examples. Attention is drawn to importance of culmination point along a fold hinge line. Sheath and eyed folds are described as separate entities formed by different mechanisms. Late stages in the development history of folds are explained by using deformed physical models. Significance of buckle shortening and layer parallel strain across fold profiles is highlighted. Development of boudins, normal, and thrust faults on fold limbs are discussed. The sequence of deformation suggests that the second order folds should not be described as parasitic folds because the term does not have a correct genetic implication. The chapter highlights the importance of folding in mountain building and how a clear understanding of early and superposed folding can help in resolving the complete deformation history of a region.