DOME, BASIN, PERICLINES

This is formed when early and late folds are both upright with subvertical axial planes, the latter making a large angle with each other. The axes of early and late folds are also at large angle to each other. The domes and basins are not ideal but are elongated in the form of elliptical domes and elliptical basins depending upon which folding is more intense. The domes and basins will appear elongated in the direction of early fold axial traces if the intensity of late folds is very mild and that of early folds very strong. The reverse can also be true.

The result is the formation of dome and basin outcrop pattern. On denudation, they have the forms of eye shaped outcrops owing to the intensity of one fold set being greater than the other. When antiforms of early folds cross with antiforms of late folds, mutual culmination gives rise to a domal structure. When synforms of the two generations cross each other mutual depression gives rise to a basins. When early antiforms are crossed by later synforms, the antiformal hinge of early fold is depressed and when a synform of early generation is superimposed by an antiform of later generation it causes culmination of the local synformal hinge giving rise to structures called periclines. The photograph below shows the periclines in the Zagros Mountains of Iran on regional scale, this picture being a satellite photograph.