FIELD BASED STRUCTURAL OBSERVATION OF DOME GEOMETRY AND KINEMATICS, TALLULAH FALLS DOME, GEORGIA

The Tallulah Falls dome (TFD) is located northwest of the terrane bounding Brevard Fault, within the Eastern Blue Ridge thrust sheet. The goal of this study is to describe the geometry of the TFD and kinematics associated with dome formation from a field perspective. We present new field observations along with existing published and unpublished data in order to determine spatial relationships and structural trends within and around the TFD.

The TFD has a long axis of 25 kilometers and axial ratio of 1:1.5, indicating it is a prominent orogen-parallel map-scale structural feature of the Southern Appalachians. Timing of emplacement has not been directly determined, however, previous authors have suggested an Alleghanian emplacement age based on Ar-Ar closure ages in amphibole and muscovite, and structural similarity with other Alleghanian domes. The TFD is cored by the Tallulah Falls Quartzite and Muscovite Schist, which sit structurally below the Tallulah Falls Formation, an amphibolite grade meta-sedimentary sequence. Grenville-aged metaplutonic basement gneisses are found near the dome boundaries, both inside and outside of the dome. Lineations within the dome are sub-horizontal in the core and plunge away from the core near the dome boundary. A complex pattern of shear is recorded by S-C fabrics and porphyroclasts within the dome. Isoclinal folds persist throughout the surrounding Tallulah Falls Formation, whereas foliation and bedding within the TFD are sub-horizontal to horizontal with minor folds, and plunge 30⁰-40^o away from the core near the dome boundary.

We constructed an orogenic perpendicular cross-section using field observations and measurements. Interpretations of dome geometry based on bedding and foliation are nearly identical; we therefore conclude that bedding attitudes are sub-parallel to parallel with foliation orientations, implying either transposition of bedding, or bedding perpendicular flattening. We prefer the latter, due to the absence of isoclinal folding within the dome. Contrasting outcrop scale folding inside and outside of the dome, along with dome boundary truncation of unit scale folding patterns, suggests that the TFD experienced a different strain history than the surrounding terrane.