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The Blue Ridge and Great Valley of western Virginia are part of a detached master thrust sheet that extends through the central-southern Appalachian change of trend and has a root zone situated east of the Blue Ridge under the Piedmont. The mapped Pulaski fault and North Mountain fault crop out in the Great Valley as splay faults terminating in thrust tip anticlines and merge at depth with the buried master detachment floored primarily in Upper Ordovician Martinsburg Shales. Overall transposition of the thrust sheet from the root zone indicates that as much as 32 km (20 mi) of displacement may be translated westward into the Valley and Ridge proper and Allegheny Plateau as initial cover shortening above the Martinsburg Shale. Within the Great Valley and into the Roanoke recess at the juncture of the central and southern Appalachians, much of the cover shortening of this master sheet is accommodated by the Pulaski and North Mountain faults. From northeast to southwest, movement on the outcropping and buried master segment of the North Mountain fault decreases, and the surface fault terminates in southern Rockbridge County. Displacement on the Pulaski fault increases from northeast to southwest, and we infer that it assumes the decreasing displacement on the outcropping and buried segments of the North Mountain fault by displacement transfer.

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