Comparisons of mechanical and kinematic models of fold-and-thrust belt structures

Abstract:

Understanding the geometry and temporal evolution of fold-and-thrust belts is essential to many scientific and societal applications, including regional tectonic studies, petroleum exploration, and seismic hazards. Several modeling methods have been developed to aid in their interpretation, which generally fall into end-member kinematic and mechanical approaches. Kinematic models provide geometric predictions of the relationships between fold and fault shape based upon first-order assumptions, yet are often too simplified to be applicable to real structures; in contrast, mechanical models investigate how rocks with defined physical properties might deform under assumed constituitive relationships and applied boundary conditions, yet are dependent on assumed values for rock properties, and are often not essentially predictive of specific structures. However, neither of these perceived shortcomings are insurmountable, and indeed, both can be addressed through comparing more sophisticated modeling approaches against each other.

We demonstrate this by comparing a series of model results from both methods. First, we explore a range of discrete element mechanical models with different material properties and strain rates, and investigate the role that these parameters have on overall fold-and-thrust belt properties and the styles of structures that comprise the fold-and-thrust belts that result. Second, we focus on mechanical models of individual shortening structures that deviate from the traditional kinematic assumptions of structural geometry and demonstrate that a modified numerical kinematic approach may be employed to provide an accurate representation of the growth of the structures. By relating variations in fault geometries and rock properties with the parameters in the best-fitting kinematic models, we are able to determine relationships between these variables, defining mechanically-informed ranges of likely kinematic model parameters that can be used with confidence in application to natural structures. We demonstrate that this more flexible velocity-based description of kinematic fault-related folding can be further integrated with erosion, subsidence, and growth strata deposition, permitting even more realistic representation of natural fold-and-thrust belt systems.