Macroscopic polyphase folding illustrated by the Toxaway dome, eastern Blue Ridge, South Carolina-North Carolina

摘要

The Toxaway dome is located in the Blue Ridge of North and South Carolina immediately northwest of the Brevard zone. It is composed of a core exposing banded granitic gneiss (Toxaway Gneiss, formerly Whiteside Granite) and a sliver of Tallulah Falls Formation rocks. The dome is flanked on all sides by rocks of the Tallulah Falls Formation. The Toxaway dome in its general outcrop pattern is an elongate feature that has a steeply northwest-dipping northwest limb and a more moderately inclined southeast limb. At the ends, the structure plunges gently northeast and southwest. Detailed mapping of the core of the dome in South Carolina reveals that the sliver of Tallulah Falls Formation rocks has a hooked outcrop pattern, and is completely isolated in outcrop from the main mass of Tallulah Falls Formation rocks surrounding the dome. At least two episodes of flowage folding have been recognized in the Toxaway dome. The first set is isoclinal and recumbent, trending east to northeast and verging north to northwest. The second set is more upright and may be isoclinal to open, trending northeast and verging northwest. Later mesoscopic crenulation cleavage and macroscopic northeast- and northwest-trending flexural-slip folds are also present. The Toxaway dome is an F₂ feature produced by refolding of earlier F₁ recumbent isoclines. The structural sequence recognized here is much the same as that observed in the Blue Ridge, Chauga belt, and Inner Piedmont. This is probably also the same structural sequence that can be observed throughout the Blue Ridge.