Rotation of fabric elements in convergent shear zones,with examples from the southern Appalachians

Plane-strain shear zones between rigid walls which do not rotate but which converge and move laterally relative to each other are here-in referred to as convergent shear zones. Analysis of the deformation in convergent shear zones indicates the existence of two flow apophyses, one parallel to the shear zone wall and the other inclined to the wall. Modeling of the development of fabrics in convergent shear zones indicates the occurrence of stable orientations in which S and C′ do not rotate and are oppositely inclined to the shear-zone boundary. The stable C′ orientation is parallel to the inclined flow apophysis and also is parallel to the approach velocity vector of the opposing walls of the shear zone. If it can be demonstrated from field relationships that the walls of a shear zone were rigid and remained parallel, then the occurrence of a flow apophysis inclined in the direction of shear is diagnostic of convergent shear. S and C′ fabrics in the Ridge Road and Gundy Creek shear zones of the southern Appalachian Piedmont are interpreted to indicate a convergent shear regime with an approach velocity vector oriented ~ 10–13 ° clockwise from the strike of the zones.