Fold mountains are mountains formed mainly by the effects of folding on layers within the upper part of the Earth's crust. In the time before either plate tectonic theory developed, or the internal architecture of thrust belts became well understood, the term was used for most mountain belts, such as the Himalayas. The term is still fairly common in physical geography literature but has otherwise generally fallen out of use except as described below. The forces responsible for formation of the fold mountains are called orogenic movements. The term orogenic has derived from a Greek word meaning mountain building. These forces act at tangent to the surface of the earth and are primarily a result of plate tectonics.
Fold mountains are formed when two tectonic plates move together (a convergent plate boundary). Fold mountains are usually formed from sedimentary rocks which accumulated along the margins of continents. When plates and the continents riding on them collide, the accumulated layers of rock may crumple and fold like a tablecloth that is pushed across a table, particularly if there is a mechanically weak basal layer such as salt.
- The Jura mountains - A series of sub-parallel mountainous ridges formed by folding over a Triassic evaporite decollement due to thrust movements in the foreland of the Alps.
- The 'Simply Folded Belt' of the Zagros mountains - A series of elongated anticlinal domes, mostly formed as detachment folds over underlying thrusts in the foreland of the Zagros collisional belt generally above a basal decollement formed in the Neoproterozoic Hormuz evaporite.
- The Akwapim-Togo ranges in Ghana
- The Ridge-and-Valley Appalachians in the Eastern United States.
- Ulmer, S. (11 August 2011). "Fold mountains slip on soft areas". ETH Life. ETH Zürich. Retrieved 21 February 2012.