Fold (geology)
geological structure / From Wikipedia, the free encyclopedia
Rock often deforms in such a way that it bends instead of breaking. This is called a fold. The term fold is used in geology when one or a stack of originally flat, level surfaces, such as sedimentary strata, are bent or curved as a result of pressure and high temperature. The basic cause is likely to be some aspect of plate tectonics.
When two forces act towards each other from opposite sides, rock layers are bent into folds. How folds are formed due to compression is known as folding. Folding is one of the endogenetic processes; it takes place within the Earth's crust.
Folds in rocks vary in size from microscopic crinkles to mountain-sized folds. They occur singly as isolated folds and in extensive fold trains of different sizes, on a variety of scales. A set of folds distributed on a regional scale constitutes a fold belt, a common feature of orogenic zones.
There are large-scale and small-scale folds. Large-scale folds are found mainly along a collision boundary between two tectonic plates.