THE DAHLONEGA GOLD BELT AND HILLABEE GREENSTONE: EVIDENCE FOR FAST-PACED TACONIC TECTONISM IN THE EASTERN BLUE RIDGE?

High precision, Ordovician (470ma) U-Pb zircon age dates from felsic volcanics of the Hillabee Greenstone (HG) in NE Alabama: (McClellan and Miller, 2000) and in the Dahlonega Gold Belt (DGB) in NE Georgia (Thomas and Miller, in review) require new ideas to explain the evolution of accreted terrane(s) of the eastern Blue Ridge (EBR). In NE GA, the DGB metavolcanics, metasediments, and associated gold and volcanogenic massive sulfide (VMS) deposits have traditionally been viewed as late Proterozoic to early Paleozoic, rift or back arc materials deposited on the trailing edge of Laurentian crust during the development of the Iapetus Ocean. In contrast, similar lithologies and VMS/gold deposits of the HG in NE AL have been proposed on the basis of stratigraphic correlation to represent an early to middle Devonian arc sequence linked to Laurentia. The new Ordovician ages and other studies in the EBR suggest these two volcanogenic sequences may have formed by fast-paced Taconic subduction back-arc volcanism and subsequent tectonic events. The contrasting metamorphic grades of the two sequences would likely require significant transpressional faulting of different portions of an evolving arc boundary to achieve their current positions along the northwest edge of the eastern Blue Ridge terrane boundary. The complexly deformed stratigraphy of the DGB preserves such evidence. The rapid pace of tectonism in the NE GA EBR is also indicated by the nearly coeval Ordovician ages of peak metamorphic assemblages and a synkinematic intrusive from the Hayesville thrust sheet northwest of, and overlying the DGB. The Hayesville fault and DGB are overprinted by a younger, as yet undated metamorphic event of lower amphibolite grade, and the DGB is fault bounded to the SE by the still younger, Acadian-age Chattahoochee thrust sheet, providing further constraints on the timing of EBR terrane assembly.