Field based study of thrust faults in the Appalachian Valley and Ridge Province Newport, Virginia

Abstract

This study focuses on a series of thrust sheets exposed in the Appalachian Valley and Ridge Province Blacksburg-Pembroke area in southwest Virginia. Structures in the hanging wall of the Saltville thrust (Saltville thrust sheet) and the footwall of the Saltville thrust (Narrows thrust sheet) are examined. The first part of this study involves the construction of a series of thrust transport-parallel 1:24,000 scale geologic cross sections to constrain the subsurface geometry of fault and fold structures within the Saltville and Narrows thrust sheets. The second part of the study involves an outcrop-scale study of geologic structures exposed along a series road cuts in the footwall of the Saltville thrust and the geometric and relative timing relationships between folding, cleavage formation and thrust faulting. The cross sections show a series of interconnected splay faults branching off of the Saltville thrust and cutting both its hanging wall and footwall. Angle of dip and magnitude of dip-slip displacement on thrust and splay faults progressively decrease from hinterland to foreland within this fault system that is referred to as the Spruce Run Mountain-Newport (SRMN) fault system. Bedding within this fault system essentially forms a structural transition zone between the Saltville and Narrows thrust sheets, defining a km-scale fractured synform-antiform fold structure that has many structural attributes usually associated with fault propagation folding. In the road cut outcrops, early meter-scale faults are folded by later foreland-(NW) vergent folds. Although cleavage defines convergent cleavage fans about these folds, subtle obliquities between folds and cleavage indicate that folding post-dates early layer-parallel shortening and associated foreland-vergent thrusting.