Fault rocks can be studied by charting how undeformed rocks near a fault transform into mylonitic or cataclastic tectonites, or by examining rock masses at different points along a fault to determine how changes in temperature, pressure, etc. affected the fault’s history. Both approaches have merit in thrust belts because thrust faults form under a range of conditions and may evolve along several different paths. Using the first approach, we distinguish two fault zone types analogous to Means’ (1984) two types of shear zones: Type I fault zones grow in thickness as movement on the fault increases; Type II fault zones initiate as zones of localized deformation, and deformation becomes further localized as displacement increases. Both Type I and Type II fault zones occur in the Appalachian fold-and-thrust belt. The second approach shows that fault rocks from the thrust zone beneath the southern Appalachian Blue Ridge and that beneath the Bay of Islands ophiolite evolved in similar ways, despite differences in rock types and local structural history. Three conclusions emerge from our survey of fault rocks from thrust faults: (1) rocks from both external and internal thrust zones may deform by fracturing or by plastic flow, and may alternate between those modes as local physical conditions change; (2) fault zones with large displacement nearly always weaken with continued displacement; (3) fluid phases are critically important to the softening processes, which accommodate large displacements in both external and internal thrust zones.

Controversy is common concerning the sequence of thrust fault imbrication on the scale of one or several quadrangles. Regional thrusting sequences in young orogenic belts are generally from the hinterland to the foreland. This is contrary to the previously proposed regional progression of thrusting for the southern Appalachian Valley and Ridge province. This paper uses cutoff-line maps to systematically examine some of the map patterns and cross-sectional interpretations used as evidence for the foreland-to-hinterland sequence of thrusting. Idealized examples of cutoff-line maps and cross-sectional patterns for both truncated structures and stair-stepped structures can be compared with observed map patterns and previously proposed cross-sectional interpretations. This provides critical evidence for interpreting the map data. Additional critical observations can be made as to the extent that faults may be folded by underlying structures, rather than truncating them. Overall, the cutoff-line approach and the folded fault approach document that the truncated folds expected in map-pattern for a foreland-to-hinterland thrust sequence do not occur in the east Tennessee area. Folded faults and westward-younging cutoff-line patterns indicate that later faults were in front of, and beneath, earlier ones in a hinterland-to-foreland sequence.