2-D and 3-D modeling of detachment folds with hinterland inflation: A natural example from the Monterrey Salient, northeastern Mexico

Geologists now recognize the presence and abundance of detachment folds in various contractional settings. Several two-dimensional geometric and kinematic models exist to describe the development of such structures. These models typically are area-balanced, are interpreted to develop by hinge migration, limb rotation, or a combination of the two processes, and possess a constant regional level outside the fold itself. We present two new two-dimensional geometric and kinematic models for detachment folds that incorporate hinge migration and limb rotation as their deformation mechanisms. These area-balanced models differ from previous models, however, in that they allow ‘hinterland inflation’ to occur, thereby creating a higher local regional level in the hinterland relative to the foreland. This local regional difference across the detachment fold may reflect hinterland uplift due to thickening of the incompetent unit, foreland deflation of the incompetent unit as material migrates into the fold core during fold growth, and/or migration of material out of the fold core as the fold tightens.We illustrate the utility of these models by constructing pseudo-three-dimensional representations of the western termination of the Nuncios Fold Complex in the Monterrey Salient, northeastern Mexico. Our results suggest that the limb rotation model more accurately portrays the overall three-dimensional fold geometry for the Nuncios Fold Complex, matches the observed hinterland inflation, and predicts more reasonable detachment depths for the structure along its length. These results agree with interpreted kinematics based on field observations and illustrate how this modeling approach may help constrain interpretations of detachment folds with hinterland inflation in areas lacking sufficient data.