STRUCTURAL EVOLUTION ALONG A MAJOR APPALACHIAN SALIENT-RECESS JUNCTION RESULTING FROM OBLIQUE COLLISIONAL CONVERGENCE ACROSS A CONTINENTAL MARGIN TRANSFORM FAULT: PART 1- GEOLOGIC SETTING

Among the most striking geometric features of the Appalachian-Ouachita orogen is the broadly sinuous nature of structural patterns along the W flank of the system, a geometry characterized by marked curvature of structure and stratigraphy into a series of regional salients (cratonward convex) and recesses (cratonward concave). The tightest Appalachian salient/recess juncture, the "Cartersville transverse zone" (CTZ) in Georgia, is the boundary between the Tennessee salient (TS) and the Alabama recess (AR), where the orogen arcs through ~125 . The CTZ is the locus of a number of significant transverse stratigraphic changes and thin-skinned transverse structures along a narrow N 44 W-trending path, extending for ~110 km highly oblique to the orogen, from the SE edge of the Plateau, southeastward to the southeastern boundary of the W. Blue Ridge-Talladega belt (WBRTB), essentially the entire width of Appalachian deformation experienced by Laurentian cover rocks. Terranes of the E Blue Ridge, SE of the Allatoona fault, exhibit no contrasts across the CTZ. Near Cartersville, Georgia, the structural grain of the frontal metamorphic allochthon (WBRTB) and the physiographic mountain front is indented more deeply (~50 km) into the interior of the orogen than anywhere else along the W flank of the S. Appalachians. Most spectacular among the thinned-skinned transverse structures is a hanging-wall lateral/oblique ramp at the base of the WBRTB, in which the upper-level detachment flat, within the Chilhowee Gp. across the AR, cuts downward several kilometers to a lower-level detachment along the TS involving Grenville basement and Late Proterozoic cover rocks. A number of stratigraphic and structural contrasts observed along the CZT suggest that many of the thinned-skinned transverse structures along it result from an initial, NW-striking right-lateral, continental margin transfer fault along the SW flank of the Late Proterozoic Ocoee rift basin involving a step of several kilometers in the level of the Grenville basement. This structure, inherited from a structural framework derived during Late Precambrian rifting along southeastern Laurentia, subsequently transitioned into a left-lateral oblique ramp during the contractional deformation associated with Alleghanian collisional events as the WBRTB allochthon was moved forward over frontal thrust ramps.