THE STRUCTURE OF MONOCLINAL FOLDS RESULTING FROM VARIABLE AMOUNTS OF OBLIQUE SLIP ALONG BASEMENT-INVOLVED FAULTS: RESULTS OF PHYSICAL MODELING

The resultant deformation of cover rocks in a basement-involved fault-related fold is dependent on many variables. Consequently, different modeling techniques are often used to forward-model a simplified fault-fold system while changing one of the variables in an attempt to predict the effects of a particular variable. One of the more difficult variables to model is strike-slip motion along the fault because this involves out of plane motion. This study uses scaled physical models of clay overlying a rigid basement with a single master reverse-fault to investigate the 3-D development of monoclinal folds that form above faults with variable strike-slip components. Only the strike orientation of the basement fault in relation to the applied displacement of the basement hanging-wall is varied between models. A close-range photogrammetric method is used to record the 3-D evolution of the fold by tracking a grid of discrete points with approximately 1 cm spacing on the surface of the clay. In addition to recording the 3-D geometry and displacement of the fold, relative displacement between adjacent points are used to calculate surface strains on the clay. While the forelimb geometry is very similar for different models with a variable strike-slip component, there are distinct displacement and strain patterns that develop on the clay surface between the different models. Assuming analogous deformation between our models and natural fault-fold systems, our modeling provides a direct relationship between strike-slip motion on a basement fault and the displacement and strain patterns that exist in natural monoclines.