Hinterland Inflation in Detachment Folds: A Natural Example from the Monterrey Salient, Mexico

M. Scott Wilkerson¹, Sara M. Smaltz¹, Dannena R. Bowman¹, I. Camilo Higuera-Diaz², and Mark P. Fischer^2
1 DePauw University, Greencastle, IN
² Northern Illinois University, De Kalb, IL

Geologists now recognize that detachment folds exist in various contractional settings, ranging from fold-thrust belts to extensional toe structures. Because such structures are increasingly becoming targets for hydrocarbon exploration, it is important to better understand their development. Numerous 2-D geometric and kinematic models exist to describe detachment folds. These models are typically area-balanced, are interpreted to develop by hinge migration, limb rotation, or some combination of the two processes, and possess a constant regional level outside the fold itself. We present new 2-D geometric models for detachment folds that incorporate hinge migration and limb rotation as their deformation mechanisms, respectively. These models differ from previous models, however, in that they allow ‘hinterland inflation' to occur, thereby creating a higher regional level in the hinterland relative to the foreland. This regional difference may reflect hinterland uplift due to thickening of the incompetent unit and/or foreland deflation of the incompetent unit as material migrates hinterland-ward during fold development.

We illustrate the application of these models by constructing pseudo-3-D representations of the western termination of the Nuncios fold complex in the Monterrey Salient, Mexico. Our results suggest that only the limb rotation model can accurately simulate the overall 3-D fold geometry, match the observed ‘hinterland inflation' produced by the lower incompetent unit, and predict reasonable detachment depths for the structure along its length. These results also show the utility of pseudo-3-D models in constraining detachment fold interpretations in areas lacking quality data and/or where the 3-D detachment geometry is unknown.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005