INVESTIGATING THE IMPACT OF MECHANICAL PROPERTIES ON CONTRACTIONAL FAULT-RELATED FOLDING STYLE THROUGH DISCRETE ELEMENT MODELING (Invited Presentation)

An understanding of the structures that compose fold-and-thrust belts is important to many practical applications, including geologic mapping, regional tectonic studies, earthquake hazard assessment, and petroleum geology. Fold-and-thrust belts have long been recognized as exhibiting a variety of fault-related-folding styles, yet the conditions that contribute to these differences are not fully understood. Thus, the ability to recognize and characterize different structural styles, and to determine the mechanical and geometric conditions that lead to the development of these differences, is essential. I will present the results of a discrete element mechanical modeling study (DEM) in which we tested the relative impact of various geometric and mechanical factors in order to explore the role and relative contributions of these conditions in determining the kind of fault-related folding structures that develop. Modeling of contractional structures under a range of boundary and material strength conditions demonstrates that (1) the major styles of contractional structures can be reproduced under realistic ranges of mechanical and boundary conditions, and (2) fundamental aspects of the mechanical strength of the deforming material (peak strength, strain weakening, and layer strength anisotropy) exert a first-order control on the style of structures that grow as deformation progresses. Observations of the distortional strains that develop in the model help to demonstrate the relative contributions of different mechanisms that accommodate the deformation, such as flexural slip and localized shear, which ultimately determine the resultant fault-related folding style. Thus, these models provide a context for understanding how rock and fault properties control the growth of geologic structures associated with long-term deformation in contractional settings.