Mechanical controls on structural styles in shortening environments: a discrete-element modelling approach

Abstract It has long been recognized that the structures that accommodate shortening within fold-and-thrust belts exhibit a wide variety of styles that reflect the mechanical behaviour of the stratigraphic units that are being deformed. The ability to characterize these different structural styles, and to understand the factors that control their variability, is essential to many applications, including petroleum geology, earthquake hazard assessment and regional geological studies. The relative contributions of different aspects of the mechanical stratigraphy and boundary conditions to determining fault-related folding style are investigated through the use of the discrete-element modelling (DEM) method in this study. Modelling emergent contractional structures within a shortening wedge with this method demonstrates that (a) The major different styles of shortening structures can all be reproduced under different mechanical circumstances within the range of realistic mechanical conditions, and (b) Different aspects of the mechanics of the deforming rock units (for example, peak strength, strain weakening, layer strength anisotropy) exert various degrees of control on the styles of structures that emerge from the models as shortening progresses. These analyses inform our understanding of the relative importance of these different factors in determining the style of structures which accommodate shortening in different fold-and-thrust belt systems.