Polyharmonic Folds

Polyharmonic folds developed in banded hornblende-biotite-quartz-feldspar gneisses, Swiss Alps. This multilayer sequence is considered polyharmonic because the axial planes of the folded thin layers (parisitic folds) are parallel to the axial plane (red) of the larger structure. The parisitic folds are Z-shaped and asymmetrical above the main axial plane, M-shaped and symmetrical in the hinge region, and S-shaped and asymmetrical below the main axial plane. Photo credit: John Ramsay.