Kinematic model of detachment folding including limb rotation, fixed hinges and layer-parallel strain

Abstract

Detachment anticlines formed above a stratigraphically fixed detachment horizon and without thinning in the syncline will, in general, require layer-parallel shortening. A kinematic model for detachment folds is presented that has planar limbs and is area-balanced but requires bed-length changes that can be expressed as layer-parallel strain. The fold grows primarily by limb rotation, not by limb lengthening at constant dip. The kinematic evolution of the geometry and strain is examined. Fold geometry is well predicted and the strain estimated in applications of the model to two map-scale detachment folds; a triangle zone from the front of the Wyoming thrust belt and a duplex-cored anticline from the Appalachian Plateau.