Fold mountain

Convergence of two continental plates.

Even when mountains are worn down, the evidence is there in the remaining rocks in Millook, Cornwall

Zagros Mountains seen from space.

A fold mountains is a mountain that is formed mainly by the effects of folding on layers in the upper part of the Earth's crust. The term is rather out of date but is still fairly common in physical geography literature.

Bfore plate tectonics became well understood, the term was used for mountain belts, such as the Himalayas, which are not caused by the folding of the Earth's crust. The main mechanism that causes a thickening of the crust at the sites of collisions between continents along their boundaroes is thrust faulting.

Fold mountains are formed when two tectonic plates move together (a convergent plate boundary). Fold mountains are usually formed from sedimentary rocks that accumulated along the margins of continents. When plates and the continents that ride 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 mechanicallyweak-basal layer such as salt.

Examples

• The Jura Mountains are a series of sub-parallel mountainous ridges formed by folding over a Triassic salt bed from thrust movements as the Alps pushed into Europe.
• The 'Simply Folded Belt' of the Zagros Mountains in Iran has both thrusts and folds occurring. The mountain range, about 1,500 km long, formed only in the past 5.000.000 years. Oil reserves and huge salt deposits are rising up from the subsurface. They emerge as salt "glaciers". That and their regular folding make those mountains unique in the world.
• The Akwapim-Togo ranges in Ghana
• Part of the Appalachians, in the Eastern United States, is known as the "Ridge-and-Valley Appalachians".

Related pages

• Fold (geology)