THE ASSOCIATION OF ANTITHETIC LOCAL STRUCTURES WITH CROSS-OROGEN TOPOGRAPHIC LINEAMENTS IN THE CAROLINA TERRANE, NORTH CAROLINA

The Dutch John anticline is a small fold on the eastern limb of the regional New London syncline (or synclinorium) in the Carolina terrane of central North Carolina. The geology here includes the lower section of the Cambrian Albemarle volcanic arc, which includes argillite and felsic volcanic rocks of the Tillery Formation and felsic and mafic volcanic rocks of the overlying Cid Formation, all metamorphosed in greenschist facies. The fold is asymmetric, verges southeast, and is gently plunging. Axial planar cleavage has a general orientation of about 225°,65° (RHR). Multiple scales of parasitic folds of bedding show geometries consistent with the larger anticline. Folding, bedding rotation, and cleavage have produced a strong northeast-southwest bedrock anisotropy reflected in stream and interfluve geomorphology. Unlike parts of the Carolina terrane adjacent to the Gold Hill shear zone (west of the study area), no persistent post-cleavage ductile structures (secondary foliation, superposed folds) have previously been reported here. However, we report antithetic younger crenulations associated with northwest-southeast trending fractures and major topographic lineaments. The lineaments parallel Mesozoic dike trends here and in much of the Piedmont. Their geomorphic expression is strong because of resistant metarhyodacite-capped ridges and intervening valleys, some of which expose underlying argillite. In lineament valleys, cm-scale crenulations, monoclines, and kink-like flexures plunge northwest where viewed on northwest-dipping phyllitic argillite bedding and cleavage. Some of these flexures have axial planes parallel to the dominant set of northwest-trending joints in this area, and some of the folds have joints as their axial surfaces. We tentatively suggest that these subtle post-cleavage structures are part of a tectonothermal sequence that includes fracturing and, ultimately, diabase emplacement in the upper lithosphere. Limb asymmetries of some folds indicate differential vertical displacement along southwest-northeast vectors. These small structures may be mechanically consanguineous with a ductile-brittle transitional event leading to rifting.