The western Blue Ridge Province of the southern Appalachians contains a rich record of the Mesoproterozoic Grenville orogeny, but subsequent Paleozoic metamorphic events have variably overprinted Grenville rocks, and Paleozoic thrusting has telescoped Grenville rock units. Effects of Paleozoic orogenesis must be unraveled to decipher the Grenville record. The Grenville rocks in the Blue Ridge of northwestern North Carolina and eastern Tennessee reside in a stack of Alleghanian thrust sheets that lie above the Grandfather Mountain and Mountain City windows. The composite Fries thrust sheet is the structurally highest unit in the stack and contains rocks of the eastern Blue Ridge juxtaposed against Grenville basement rocks (Pumpkin Patch Metamorphic Suite) along the Devonian Burnsville fault, which is the only identifiable Acadian structure in the thrust stack. West of the Grandfather Mountain window, the Sams Gap–Pigeonroost thrust splays off the Fries fault. Only the Fries and Sams Gap–Pigeonroost sheets appear to have been affected by Ordovician Taconic metamorphism. Below the Fries and Sams Gap–Pigeonroost sheets, Grenville basement rocks in the Fork Ridge and Linville Falls–Stone Mountain thrust sheets display widespread greenschist-facies metamorphism and deformation associated with Alleghanian thrusting. The lowest basement sheet is the Little Pond Mountain thrust sheet, which experienced only Late Paleozoic chlorite-grade metamorphism. Palinspastic restoration of the Grenville rocks to their pre-Paleozoic relative positions places rocks of the Pumpkin Patch Metamorphic Suite outboard of western Blue Ridge Grenvillian rocks.

The Burnsville fault juxtaposes Precambrian Laurentian crust and the Ashe metamorphic suite within the Fries thrust sheet of the Blue Ridge thrust complex of western North Carolina. The Burnsville fault and adjacent Ashe metamorphic suite accommodated high strain at amphibolite facies (~700 °C and ~9 kbar) during the Acadian orogeny and then were tilted southeast during Alleghanian thrusting. Deformation resulted in three kilometer-scale structural domains: the Burnsville fault dextral strike-slip domain, the “transitional” domain, and the Otter Knobs domain. Structures recording the finite flattening plane are subparallel; those southeast of the Burnsville fault shear zone are rotated counterclockwise by ~10°–15°, consistent with a component of dextral shear. Across strike into the transitional domain, shear sense indicators become scarce, fabric grades to S > L, and lineations change from subhorizontal to downdip. Across strike into the Otter Knobs domain, lineations grade to moderately southwest-plunging, and the orientation distribution of poles to foliation indicates moderately southwest-plunging folding. The macroscale Otter Knobs fold, a tight-to-isoclinal synform in which the hinge line, associated lineations, and minor fold hinges plunge moderately southwest, is interpreted to represent this structural element. No evidence of oblique or reverse shear is observed. The across-strike changes between these coeval domains are consistent with heterogeneous wrench-dominated (10°–20° from the plate boundary) transpression. Changes across strike from the Otter Knobs domain into the transitional domain record part of the deformation path for a zone with an “effective” convergence angle of 14°–18°, including the rotation of structures recording the maximum incremental stretch.

Abstract Recent field and associated studies in eight 7.5-minute quadrangles near Mount Rogers in Virginia, North Carolina, and Tennessee provide important stratigraphic and structural relationships for the Neoproterozoic Mount Rogers and Konnarock formations, the northeast end of the Mountain City window, the Blue Ridge–Piedmont thrust sheet, and regional faults. Rocks in the northeast end of the Mountain City window constitute an antiformal syncline. Overturned Konnarock and Unicoi formations in the window require a ramp-flat geometry in the hanging wall of the Blue Ridge thrust sheet or stratigraphic pinch-out of the Konnarock Formation. Undulose and ribbon quartz, fractured feldspars, and mylonitic foliations from the Stone Mountain and Catface faults indicate top-to-NW motion, and ductile deformation above ∼300 °C along the base of the Blue Ridge thrust sheet on the southeast side of the window. The Stone Mountain fault was not recognized northeast of Troutdale, Virginia. The Shady Valley thrust sheet is continuous with the Blue Ridge thrust sheet. The ∼750 Ma Mount Rogers Formation occurs in three volcanic centers in the Blue Ridge thrust sheet. Basal clastic rocks of the lower Mount Rogers Formation nonconformably overlie Mesoproterozoic basement in the northeasternmost Razor Ridge volcanic center, but the basal contact in parts of the Mount Rogers and Pond Mountain volcanic centers is strongly tectonized and consistent with a NW-directed, greenschist-facies high-strain zone. The contact between the Mount Rogers Formation and Konnarock Formation is nonconformable, locally faulted. Metarhyolite interbedded with lacustrine and fluvial rocks suggests that volcanism and glaciation were locally coeval, establishing an age of ∼750 Ma for the Konnarock Formation, a pre-Sturtian glaciation. Multiple greenschist-facies, high-strain zones crosscut the Blue Ridge thrust sheet including the Fries high-strain zone (2–11 km wide). Foliations across the Fries and Gossan Lead faults have similar orientations and top-to-NW contractional deformation.