Thrusts in the crystalline core of the southern Appalachians formed by both ductile and brittle mechanisms during three or more major Paleozoic deformational-thermal events (Taconic, Acadian, Alleghanian), in contrast to thrusts in the foreland which formed primarily as brittle faults during the Alleghanian. Early prethermal peak thrusts formed in the crystalline core, then were subsequently thermally overprinted and annealed. Thrusts that formed late in a metamorphic-deformational sequence have maintained a planar geometry. Many of these thrusts, such as the Brevard and Towaliga faults, were later reactivated in either the ductile or brittle or both realms, possibly involving both dip-slip and strike-slip motion. The thrusts framing the Pine Mountain and Sauratown Mountains windows formed both pre- and post-thermal peak. The pre-thermal peak Box Ankle thrust in the Pine Mountain window is a structurally lower fault, whereas the window is flanked externally by the post-thermal peak Towaliga (northwest) and Goat Rock (southeast) faults. Conversely, in the Sauratown Mountains the brittle Hanging Rock thrust frames an inner window beneath the older Forbush thrust. Here a downward and outward propagating sequence is suggested for the development of thrusts. North American basement rocks are involved in both the Pine Mountain and Sauratown Mountains windows, and basement and cover behave as a homogeneously coupled mass with respect to strain. Consequently, the only factor that controlled the siting of early thrusts may have been the depth to the ductile-brittle transition zone. The frontal Blue Ridge thrust was the last formed in the Blue Ridge-Piedmont thrust sheet although the Cartersville-Miller Cove thrust is a slightly older Alleghanian thrust than the Great Smoky fault.

Abstract The Cartersville fault is exposed near the powerhouse at the base of Carters Dam located in southeastern Murray County, approximately 60 miles (96 km) north-northwest of Atlanta on the Oakman 7½-minute Quadrangle (Fig. 1). To reach Carters Dam, travel north from Cartersville on U.S. 411 until you see the signs for the Carters Dam powerhouse.

Abstract The type locality of the Pumpkinvine Creek Formation is located on I-75, approximately 32 mi (51 km) north of downtown Atlanta, and approximately 1.5 mi (2.4 km) north of where I-75 crosses Lake Allatoona (Fig. 1). Outcrop is readily apparent on both sides of the highway, but exposures of the Pumpkinvine Creek Formation are more extensive and less weathered on the east side of the highway. Do notattempt to cross the highway.

Abstract One of the best exposures of the Brevard fault zone is located along I-285 approximately 12 mi (19 km) west of the center of Altanta, Georgia. This exposure is present just south of the Chattahoochee River (Fig. 1) on both sides of the Interstate. The outcrop on the east side of the Interstate is better for examining the textures and structures of the Brevard zone. Traffic along this section of Atlanta's Interstate system is very heavy, and extreme caution should be used in viewing this outcrop.

The southwesternmost exposures of Grenville-age basement in the Appalachian Blue Ridge are present in rootless anticlinoria that lie along the western margin of the Blue Ridge thrust sheet in north-central Georgia. The southernmost of these massifs, the Corbin Gneiss Complex, lies in the core of the Salem Church anticlinorium, while farther to the north, the Fort Mountain Gneiss is exposed in the core of a smaller, unnamed anticlinorium. Both the Corbin Gneiss Complex and the Fort Mountain Gneiss are mantled by thick sequences of predominantly clastic rocks of the Ocoee Supergroup. Those clastic rocks lying nonconformably on basement gneisses, the Pinelog and Parr-Branch Formations, respectively, clearly were derived from the gneisses themselves and are probably lithostratigraphic equivalents of the Snowbird Group, basal member of the Ocoee Supergroup. Conformably overlying these coarse clastics are graphitic phyllites, metaconglomerates, and sandy marbles of the Wilhite Formation. While relict textures related to Grenville-age granulite facies metamorphism still persist locally in the basement gneisses, no evidence of this event is apparent in the cover rocks. However, all aforementioned rocks show evidence of an episode of mid-Paleozoic regional metamorphism that retrograded earlier-formed, higher temperature mineral assemblages in basement rocks. Coincident with Paleozoic metamorphism was development of overturned to recumbent isoclinal folds (F 1 ) with well-developed axial-planar schistosity. Subsequent deformational events (1) fold earlier structures, (2) deform isograds formed during the Paleozoic metamorphism, and (3) are at least partially responsible for the arcuate trace of the Great Smoky fault 1 in this area.

For many years, the question regarding what happens to the rocks of the Talladega belt in the vicinity of their apparent northeastern terminus near Cartersville has been the subject of controversy. This has coincided with the debate over the age and correlation of metasedimentary rocks that overlie the billion-year-old Corbin gneiss complex to the east of Cartersville. Both of these problems are interrelated, and the resolution of each is dependent on the other. Stratigraphic relationships in the polydeformed rocks exposed in the Salem Church anticlinorium east of Cartersville indicate that the rocks unconformably overlying the Corbin gneiss complex are lithostratigraphic equivalents of the lowermost Ocoee Supergroup. These lithologies can be traced southwestward to the area east of Emerson where the Talladega belt has been presumed to end. Here, it is evident from studying the small- and large-scale structural features that folding has played an important role in the structural and stratigraphic complications that occur. Our mapping suggests that although part of the Ocoee Supergroup does disappear southwest of Cartersville because of folding, other parts of the Ocoee continue on to the southwest and into the Talladega belt. In the Talladega belt of Alabama, rock units such as the Heflin Phyllite, Abel Gap Formation, and Lay Dam Formation are lithologically similar but may be much younger than parts of the lowermost Ocoee Supergroup sequence present in Georgia. Other rock units of the Talladega belt in Alabama also resemble parts of the Ocoee sequence, but they too are not directly relatable to the Ocoee. AH long-range correlations can be considered only speculative until detailed mapping in western Georgia and eastern Alabama is completed. However, there is evidence to suggest that at least part of the Talladega belt is Precambrian in age and was deposited synchronously with the Ocoee Supergroup.

This study documents an eruptive center, the instrusive Flat River complex and associated Carolina slate belt volcanic rocks near Durham, North Carolina. The zircon Pb/U age of the granite, granodiorite, quartz diorite, gabbro Flat River complex is 650 ± 30 m.y. Local vent breccias, chilled and protoclastically deformed margins, and petrographic comparisons with the experimental results in the qz-ab-or system confirm that the Flat River complex was emplaced at a depth of less than 1 km and was locally surface breaking. Thus, the Flat River can be viewed as a very shallow fossil volcanic magma chamber and may be typical of many granitoid plutons in the Carolina slate belt. The Flat River was intruded into a pile of coarse, near-vent pyroclastic deposits and lavas of felsic to intermediate composition. Intercalated in these is an exhalative unit of thinly layered to laminated metachert and iron oxide. Shallow to deep (or quiet) probably marine conditions prevailed. Some subaerial pyroclastic rocks may be present in the older parts of this >650-m.y. to 620-m.y.-old sequence of volcanic rocks.