Displacement transfer at thrust terminations: the Saltville thrust and Sinking Creek anticline, Virginia, U.S.A.

Abstract

The Saltville thrust terminates in the core of the Sinking Creek anticline. Changes in the amplitude of the anticline may preserve profile shortening as the thrust displacement decreases towards the fault termination. Consequently, thrust displacement would be transferred into the fold. We combine newly published maps and new strain and mesostructural data from the Tuscarora Sandstone to argue that the Sinking Creek anticline did perform this kinematic role. We propose that the anticline developed as a fault-propagation fold that experienced both décollement and anticlinal breakthrough by the Saltville thrust. Thrust displacement was accommodated by the development of the modified fault-propagation fold and by transfer to a roof flat from the décollement breakthrough. New strain and mesostructural data indicate no fixed pin lines in either the hinge or backlimb throughout folding. Consequently, layer slip occurred through the hinge during folding and the forelimb deformed internally during breakthrough. Towards the plungeout of the Sinking Creek anticline, the displacement on the Saltville thrust is transferred to a floor thrust. We apply this interpretation to the termination of the St. Clair thrust, which has a similar surface geometry where the thrust terminates into an anticline. A testable implication of this proposed interpretation for the St. Clair thrust is that the Appalachian Plateau must absorb over 20 km of thrust displacement as horizontal shortening.