PROVENANCE AND TIMING OF CRUST FORMATION IN THE SOUTHERN APPALACHIAN CRYSTALLINE CORE: EVIDENCE FROM DETRITAL ZIRCON STUDIES

Recent detrital zircon studies of greenschist to amphibolite grade metasedimentary units from the Blue Ridge (BR) and Inner Piedmont (IP) of GA-NC-SC-TN provide insight into the provenance, timing, and addition of crust in the southern Appalachian orogen. Neoproterozoic to Early Cambrian rift-related, clastic sediments of the western BR contain 1.3-1.0 Ga and lesser 1.4, 1.5, and 1.9 Ga zircons. The youngest unit in the western BR, Lower Ordovician Mineral Bluff Formation, yielded detrital zircons of 1.3-1.0 and 1.4 Ga, with single grain analyses of 2.7, 2.1, 1.9, 1.8, 1.7, and 1.6 Ga. The central BR consists of the amphibolite to granulite grade terranes between the Hayesville and Chattahoochee-Holland Mountain (CHMF) faults. Collectively, these terranes are dominated by 1.3-1.0 Ga and lesser amounts of 2.7, 2.3, 1.8, 1.6, 1.5, 1.4, and 0.7 Ga detrital zircons. The Tugaloo terrane extends from the CHMF to the Brindle Creek fault encompassing the eastern BR and western IP. This amphibolite grade terrane is dominanted by 1.3-1.0 Ga zircons and minor 1.6 and 1.4 Ga zircons. A xenolith of biotite gneiss from the ~1.15 Ga Wiley gneiss contains 1.1-1.2 Ga rims marking new rim growth associated with intrusion, and unaltered 1.3 and 1.5 Ga cores. A sample from the Smith River allochthon near Ararat, NC, yielded abundant 1.3-1.0 Ga zircons and lesser amounts of 1.4, 0.7, and 0.47-0.43 Ga zircons. The Cat Square terrane contains a unique assemblage of 2.7, 2.3, 1.4, 1.1, 1.0, 0.6, and 0.46-0.42 Ga zircons.

Dominance of 1.3-1.0 Ga ages in all samples suggests a significant contribution from and recycling of a Grenville source from the Neoproterozoic until the Early Devonian. Presence of 0.7 Ga zircons with Eu/Eu* anomalies is compatible with A-type Crossnore and Robertson River plutonic suites, and link 1.3-1.0 Ga zircons to Grenville basement in the southern and central Appalachians. Archean and Paleoproterozoic ages from the central BR may represent distal sediment input from the Laurentian mid-continent or sourced from Amazonia during or after rifting. Ordovician detrital zircons from the Smith River allochthon constrain maximum age of depostion and timing of metamorphism to post-Mid. Ordovician. Mixed Gondawanan and Laurentian affinity Cat Square terrane provenance represents the remnants of the Rheic ocean, closed by Devonian accretion of the Carolina superterrane.