Mountain Building

Folding

Folding is frequently seen during mountain building. There are many types of folds from microscopic to macroscopic but almost all are a result of compressional forces.

Anticlines are formed by arching or upfolding of rock layers. In an anticline, the oldest rock layers are found in the center of the fold.

A syncline is created by the downfolding of rock layers until a trough is formed. In a syncline, the youngest rock layers are found in the center.

Anticlines and synclines can be symmetrical, asymmetrical or asymmetrical overturned. An asymmetrical overturned fold occurs when one limb is tilted beyond vertical. It is also important to note that anticlines and synclines plunge on their edges.

Monoclines are large step like folds found in horizontal sedimentary strata.

Domes are circular or elongated structures generated when basement rock upwarps to deform overlying sedimentary strata.

Basins are also circular or elongated structures, but they are generated by the downwarping of basement rock. In basins, the oldest rock is found along the edges of the basin while the younger rock is found in the center of the basin.