Kinematics of detachment folding, Appalachian Valley and Ridge, West Virginia

This study assesses the geometry and kinematics of a fold at the east edge of the Nittany Anticlinorium, Appalachian Valley and Ridge Province, West Virginia. Regional deformation consists of minor to major folds within two vertically stacked thrust sheets. Geometric analysis of a first-order fold in the upper, Silurian-Devonian sheet indicates it is a detachment fold with a detachment depth of up to four kilometers. The estimated detachment depth indicates involvement of the underlying, thrusted Cambrian-Ordovician sheet in the folding. Kinematic analysis of uplifted fold area relative to measured shortening amounts does not indicate a clear relationship. Finite strain measurements of three oriented samples from a secondary fault-related fold show a burial signal and secondary simple shear in the secondary fold backlimb. An undetermined type of shear caused thickening in the secondary fold forelimb. The secondary fold geometry is more consistent with the trishear model than the kink-band model