ABSTRACT

Experimental studies of the shapes of surfaces resulting from the interference of two intersecting systems of similar folds have been carried out by means of three-dimensional models consisting essentially of vertical laminae parallel to the axial planes of the intersecting fold systems. The edges of these laminae form a continuous surface on which the cyclic anticline-syncline profiles of the component folds are produced by differential vertical shear movement parallel to the respective axial planes. The mutual interference of the component profiles results in a continuous interference surface consisting of alternating domes, basins and cols which represent the spatial relationships between centres of maximum and minimum interference. Any plane truncating such a surface exposes shapes variously transitional from linear to circular or elliptic form, and possessing both axial and quadrantal symmetry. It can be shown that sigmoid flexures, echelon alignments in a horizontal plane, and non-vertical fold axial planes can result exclusively from vertical shear movements and their mutual interference. Where such interference profiles are imposed through vertical axes on a succession of mutually inclined surfaces, the resulting successive structural closures on these surfaces do not remain centred on a vertical axis but undergo various lateral migration according to the individual dips of the surfaces. A superimposed uniform differential movement may even cause the disappearance of particular closures.