A rapid method for strain estimation from flattened parallel folds

Abstract

Superimposition of homogeneous strain on parallel folds is a potential mechanism for development of flattened parallel folds. Estimation of flattening strain by existing graphical approaches requires a large number of angular and/or linear measurements. We propose a new computer-based approach, which rapidly destrains a flattened parallel fold into a parallel fold with help of any of the commonly available graphic software. This method is based on the principle that the magnitude of flattening directly relates to change in the inherent orthogonality that exists between a tangent and an isogon, at any given angle of the limb dip, on the profile of a parallel fold. Using six examples of flattened parallel folds, we show that the results of our destraining method are consistent with those yielded by other existing methods. Besides estimating the flattening strain rapidly and involving a relatively low amount of error, our method also restores the pre-flattening fold shape without any additional geometrical or numerical operation.