Deciphering the Grenville of the southern Appalachians through evaluation of the post-Grenville tectonic history in northwestern North Carolina

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.