THE POLYGENETIC GREENBRIER FAULT, GREAT SMOKY MOUNTAINS, TN/NC

In the eastern part of the Great Smoky Mountains National Park (GSMNP), the Greenbrier fault (GF) places rocks of the Neoproterozoic Great Smoky Group (GSG) in the Greenbrier thrust sheet (GTS) onto older Mesoproterozoic rocks and Neoproterozoic rocks of the Snowbird Group. At the type-locality, the GF is a zone of brittle deformation 1 to 30 m thick that truncates bedding and stratigraphy in both the upper and lower plates. Following deposition in separate basins, the rocks of the two plates were juxtaposed along the fault, metamorphosed at greenschist to amphibolite facies, and deformed during at least two separate Paleozoic orogenic events. Away from the type locality, the contacts between the rocks of the Great Smoky Group and the underlying Mesoproterozoic gneiss, and the Snowbird and Walden Creek Groups are now interpreted as the GF. The original geometry of the GF was listric; it is spoon-shaped due to subsequent folding. In the foothills, the leading edge of the GTS is locally mapped as the Rabbit Creek fault, and the trailing edge is cut by the Hayesville fault. Preserved fault slices along the GF record faulting and folding that were pre- and(or) syn- deformation of the fault. The GF was subsequently folded during development of the F1 Copeland Creek anticline and Alum Cave syncline, and by the F2 Ravens Ford/Cataloochee anticlinoriums and the Ela/Bryson City domes. Locally the leading edge of the GTS was dismembered by the Little River shear zone and the dextral strike-slip Gatlinburg fault system. New geochronologic data support the following complex history for the GF: 1) It postdates the ca. 700 Ma deposition of the Thunderhead Sandstone of the GSG. 2) It may have originated as an extensional fault between 580 and 560 Ma, during Neoproterozoic rifting and metamorphism. 3) It predates regional metamorphism at ca. 440 Ma, and it likely had thrust motion and was folded (F1) during Taconian deformation. 4) The GTS was further transported, dismembered, folded (F2), faulted, and intruded by pegmatites from ca. 350 to 340 Ma. 5) Shear band cleavage and transposed vein quartz locally in rocks above and below the fault suggest contractional reactivation during the Alleghanian orogeny, and truncation in the subsurface by the Great Smoky fault ca. 280 Ma, and the Gatlinburg fault system in the late Cretaceous or later.