INTERFERING FOLDS IN CONSTRICTIONAL DEFORMATION

Experiments on buckle folding indicate that in pure constriction (lambda(2) = lambda(3) < 1) a dome-and-basin pattern develops in initial stages. The domes and basins do not occur along distinct rows, and with progressive deformation they do not evolve into tubular or sheath folds. The pattern is progressively replaced by diversly oriented folds with curved hinge lines. In general constriction (1 > lambda(2) > lambda(3)), there is an association of domes and basins with nonplane noncylindrical folds. The areas of domes and basins are reduced with increasing deformation. There is a dominant fold trend perpendicular to lambda(3) With a less dominant trend perpendicular to lambda(2). Folds at an angle to these two sets may also occur. The divergent folds link up in smooth arcs or join up at a dome or a basin. Over a relatively large domain the interference pattern produced by general constriction can be recognized by the association of domes and basins with nonplane noncylindrical folds, by occurrence of hair pin bends of hinge lines of open folds, by occurrence of amoeboid outcrop patterns and by absence of a consistent overprinting relation among different sets of folds. Layers subparallel to the lambda(1) axis of general constriction may give rise to two or more sets of coaxial cylindrical folds with orthogonal axial surfaces.