KINEMATIC MODEL OF DETACHMENT FOLDING INCLUDING LIMB ROTATION, FIXED HINGES AND LAYER-PARALLEL STRAIN

Detachment anticlines formed above a stratigraphically fixed detachmen t horizon and without thinning in the syncline will, in general, requi re layer-parallel shortening. A kinematic model for detachment folds i s presented that has planar limbs and is area-balanced but requires be d-length changes that can be expressed as layer-parallel strain. The f old grows primarily by limb rotation, not by limb lengthening at const ant dip. The kinematic evolution of the geometry and strain is examine d. Fold geometry is well predicted and the strain estimated in applica tions 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.