THE LEMON GAP AND SPRING CREEK QUADRANGLES, NC AND TN: INSIGHT INTO THE STRUCTURE AND METAMORPHIC HISTORY OF THE WESTERN BLUE RIDGE IN AND AROUND THE HOT SPRINGS WINDOW

Recent 1:24,000-scale mapping on the Spring Creek and Lemon Gap quadrangles reveals further evidence for Grenville metamorphism in western Blue Ridge basement units south of the Hot Springs window (HSW), and new stratigraphic relationships in the Ocoee Supergroup within the HSW. South of the HSW, the Spring Creek Granitoid Gneiss (SCGG – an interlayered sequence of biotite granitic gneiss, biotite gneiss, and amphibolite) contains unassimilated bodies of granulite facies garnet-bearing quartzo-feldspathic gneiss, quartz monzodioritic gneiss, and tonalitic gneiss. Hypersthene-bearing mineral assemblages and the presence of garnet in a recrystallized granoblastic texture characterize granulite facies metamorphism in these bodies. A strong NE-SW trending Alleghanian mylonitic fabric locally overprints the dominant NW-SE trending gneissic foliation within these granulites. Some non-granulitic layered outcrops within the SCGG show similar NW-SE trending foliations; field relationships and limited thin-section analysis suggest that foliation in these outcrops may also be a relict Grenville fabric that has not been overprinted by Paleozoic metamorphism and mylonitization. The SCGG also contains intrusive kilometer-size bodies of Late Proterozoic, olivine- and hypersthene-bearing Bakersville Metagabbro. Bakersville Metagabbro underwent both Early Paleozoic amphibolite facies metamorphism and Late Paleozoic mylonitization in this area. Southwest of the HSW, Alleghanian faults juxtapose higher-grade SCGG over greenschist facies Max Patch Granite and mylonitic metasediments of the Late Proterozoic Snowbird Group. Mylonitic metasediments are found in a NE-SW trending belt both within and proximal to the Max Patch Granite. The contact between these is either a Paleozoic thrust fault or a Late Proterozoic disconformity overprinted by Paleozoic mylonitization. Inside the HSW, recognition of established subdivisions within the Ocoee Supergroup demonstrates an unconformity between the Roaring Fork Formation (Snowbird Group) and the Sandsuck Formation (Walden Creek Group). Lack of evidence for Paleozoic faulting along the Roaring Fork-Sandsuck contact suggests that irregular rift basin topography and/or Late Proterozoic growth faults may be responsible for the missing strata.