Deformation history of the Roanoke recess, Appalachians, USA

The evolution of the Roanoke recess is controversial because agreement is lacking about the timing and continuity of deformation increments; because it may or may not have behaved like an adjacent salient and recess; because while many salients have been investigated, few recesses have; and because the role of blind thrusts is unclear. To gain insight into these controversies, we estimated shortening directions, shortening magnitudes and relative timing in the recess from map-scale folds, outcrop-scale stylolites, and grain-scale solution structures and twins. The key results from combining these new data with previous work are as follows. (1) The deformation history around the Roanoke recess is most simply described as temporally continuous with deformation migrating northeastward while the primary shortening direction rotated counterclockwise from N-directed to almost W-directed. (2) Consequently, the Roanoke recess did not deform in the symmetrical manner of the adjacent Pennsylvania salient nor with the two-step history of the Kingston recess further to the north in the Appalachians. (3) The timing and magnitude of shortening increments are sufficient to necessitate a blind thrust under the present surface rocks of the inner recess throughout the deformation history.