Nappe Formation in Part of the Southern Appalachian Piedmont

Abstract

Structural studies of rocks along the Carolina slate belt – Charlotte belt boundary reveal two generations of folding, the earlier of which is represented by a large-scale antiformal nappe. As shown by field relations and quantitative analysis of the fold geometry, this early folding began prior to metamorphism, the mechanism being largely buckling. With the onset of metamorphism and cleavage-forming process, new folds were formed and the pre-existing buckle folds were modified by compressive strain. During this time, a metamorphic gradient developed along the boundary of the two belts; as the rocks became more ductile, the large antiformal nappe was emplaced in the Charlotte belt, with its root located close to the boundary between the belts. Sillimanite-grade metamorphism in the Charlotte belt outlasted the early deformation, and some upwelling of material in this hot zone may have gently arched the nappe. Late, post-metamorphism deformation produced two sets of folds with different orientation, which appear to have a conjugate relationship, and which probably formed contemporaneously. The relation between the Charlotte and Carolina slate belts may be analogous to the infrastructure/superstructure relation commonly found in other intensely deformed mountain belts of the world.