FoldModeler: a tool for the geometrical and kinematical analysis of folds
FoldModeler is a system constructed in the MATHEMATICA(TM) environment that enables strain analysis in the profile of layers folded by the simultaneous or successive superposition of several strain patterns (layer shortening, tangential longitudinal strain, flexural flow and flattening). The fundamentals of the system involve the deformation of an initial grid of quadrilaterals according to the folding mechanisms considered. The main inputs to the system define the number, shape and size of the quadrilaterals, the characteristics of the sequences of incremental strain patterns involved, and the successive variations in form of a reference line named the 'guideline'. The main outputs of the program are the parameters defining the form of the folded guideline, the drawings of the folded layer with several markers showing the strain distribution, graphics showing the variations in the orientation of the principal directions and the aspect ratio of the finite strain ellipse as functions of the layer dip, and Ramsay's classification of the folded layer. FoldModeler has two main geological applications: (a) to predict the geometrical properties of folds produced by the combination of several types of strain patterns and (b) to analyse the strain state in specific natural quasi-symmetrical folded layer profiles and the possible combinations of strain patterns that could give rise to such a fold. This can be done by searching, with a fit and error method, a theoretical fold with the same geometrical characteristics as a given natural fold. The second application requires the existence of cleavage in the natural folded layer, and the best results are obtained when some strain measures are available. (C) 2003 Elsevier Ltd. All rights reserved.
folding strain cleavage structural geology mathematical modelling