Displacement transfer mechanisms in a portion of the Narrows/Copper Creek thrust sheet, Southwestern Virginia

Loss of displacement along the contiguous Narrows and Copper Creek thrusts in southwestern Virginia has generated a series of regional folds and second-order faults between their surface terminations. These structures form a complex system which accommodates shortening within a region where no major thrust faults exist. Displacement is transferred from the Narrows to the Copper Creek fault via a series of en echelon thrusts of smaller magnitude. Regional anticlines and synclines between and behind this thrust fault zone, however, accommodate most of the shortening. Experimental plane strain deformation of clay-plasticene multilayer analogues suggest an association between the position of regional folds and subsurface configurations of the Narrows and Copper Creek faults.

Structural analysis of mesoscopic elements indicates that early stages of deformation was accommodated by cleavage development in the Moccasin Formation, closely followed by second-order folding. Rocks of the Martinsburg and Eggleston Formations responded by localized second-order folding synchronous with cleavage development in thin shaly horizons. Regional structures formed contemporaneously with displacement of strata along the Narrows and Copper Creek thrusts. This resulted in a modification and subsidiary development of structure in the Moccasin Formation, along with a greater intensity of fabric development. The primary evolution of second-order folds within the Martinsburg and Eggleston Formations occurred at this time.