THE EARLY PALEOZOIC (TACONIC) DADEVILLE ARC COMPLEX, SOUTHERNMOST APPALACHIANS OF ALABAMA AND GEORGIA: IMPLICATIONS FOR THE CRUSTAL GROWTH OF EASTERN NORTH AMERICA

The Taconic orogeny is the first in a series of Paleozoic events responsible for the formation of the Appalachian Mountain chain. In the northern and central Appalachians, the Taconic event is heralded by the accretion/obduction of exotic (i.e., Iapetan and peri-Gondwanan) terranes onto the early Paleozoic eastern Laurentian margin; however, its presence in the southern Appalachians has long been disputed. In the southernmost Appalachians of Alabama and Georgia, the Dadeville Complex (DC) (i.e., Inner Piedmont) comprises a suspect terrane of high-grade bimodal meta-igneous and minor metasedimentary rocks cradled between Laurentian units of the eastern Blue Ridge (EBR) (e.g., Jacksons Gap Group and Opelika Complex) and Pine Mountain window. U-Pb age-dating (using LA-SF-ICP-MS) of magmatic and detrital zircons from the DC, in conjunction with previously reported geochemical, lithotectonic, and structural data, reveals that this terrane is an exotic (i.e., containing non-Laurentian ca. 880-680 Ma zircons) Late Cambrian- to Early Ordovician-aged volcanic arc complex (Dadeville arc (DA) herein) formed during Taconic orogenesis. Following its Taconic beaching, the DA was translated along Late Devonian to early Carboniferous (390-350 Ma) strike-parallel dextral shear zones. Some EBR footwall rocks yield dominant ca. 1100 Ma and sparse Ordovician detrital zircons, suggesting a minor source from the DA. The depositional ages of those footwall rocks, therefore, could constrain the timing of approachment and emplacement of the DA. Middle Ordovician (ca. 460 Ma) magmatic and/or metamorphic (Th/U= 0.001-0.48) detrital zircons in the DA overlap with high-grade metamorphism reported in the Lick Ridge eclogite and Winding Stair Gap granulite in the EBR of western North Carolina, the nearest documented outcrops containing peak-Taconic metamorphism northeast of those we report from the DC. If those Taconic events were spatially associated, a minimum of ~220 km of right-slip displacement along the Brevard zone is required. The position of the DC is tectonostratigraphically equivalent to that of the Taconic event found throughout much of the Appalachian orogen but its peculiarly internal and structurally high position make it a unique setting in which to examine the Paleozoic evolution of the southern Appalachians.