THE DOG RIVER WINDOW, ALABAMA AND GEORGIA: A FIRST-ORDER STRUCTURE IN THE SOUTHERN APPALACHIAN OROGEN

Recently the term Dog River window has been used in regional geologic map compilations of the southern Appalachians, yet it has not been properly described. The original Dog River window corresponds to the Emuckfaw Group of the eastern Blue Ridge (EBR) lying directly west of the Brevard zone. Detailed, 1:24,000 geologic mapping in the hinge and adjacent flanks of the Tallassee synform in east-central Alabama now confirms continuity of lithologies and structures of the Emuckfaw Group on the west limb with those previously assigned to the Inner Piedmont (Opelika Complex) on the east limb, greatly expanding the geographic area of the window. Distinctive metaturbidites, schists, and quartzites occur on both limbs of the Tallassee synform, and these are intruded by Middle Ordovician and younger granitoids (Kowaliga, Zana, and Farmville). Brevard zone lithologies and structures on the west limb separate the EBR from the overlying metavolcanic-metaplutonic Dadeville Complex (Inner Piedmont). In Alabama the Brevard zone lithologies are sandwiched between the syn-metamorphic Katy Creek fault, above, and the post-metamorphic Abanda fault, beneath. The Katy Creek fault traces eastward around the synform’s hinge to become the syn-metamorphic Stonewall Line shear zone that separates the Dadeville Complex, above, from the Opelika Complex, below. The Opelika Complex is bordered to the east by the Towaliga fault, which juxtaposes the Laurentian Pine Mountain window basement-cover massif, and has been referred to as the Opelika window. Since the “Opelika window” now is documented as a continuation of the Dog River window beneath the keel of the Tallassee synform, we suggest abandoning the former and retaining the latter name for the entire window. The Dog River window, recognized in its entirety, is a fundamental, first-order structure of the southern Appalachian orogen. We describe observations documenting the window and its borders and speculate on tectonic implications stemming from its recognition.