Orogeny

Young orogenic belts, in which subduction is still taking place, are characterized by frequent volcanic activity and earthquakes.

[12] The collisional orogeny may produce extremely high mountains, as has been taking place in the Himalayas for the last 65 million years.

For example, much of the basement underlying the United States belongs to the Transcontinental Proterozoic Provinces, which accreted to Laurentia (the ancient heart of North America) over the course of 200 million years in the Paleoproterozoic.

[7] A foreland basin forms ahead of the orogen due mainly to loading and resulting flexure of the lithosphere by the developing mountain belt.

The fill of many such basins shows a change in time from deepwater marine (flysch-style) through shallow water to continental (molasse-style) sediments.

[25] While active orogens are found on the margins of present-day continents, older inactive orogenies, such as the Algoman,[26] Penokean[27] and Antler, are represented by deformed and metamorphosed rocks with sedimentary basins further inland.

[29] The Wilson cycle begins when previously stable continental crust comes under tension from a shift in mantle convection.

Continental rifting takes place, which thins the crust and creates basins in which sediments accumulate.

The compressive forces produced by plate convergence result in pervasive deformation of the crust of the continental margin (thrust tectonics).

This range of fault-block mountains[36] experienced renewed uplift and abundant magmatism after a delamination of the orogenic root beneath them.

[35][37] Mount Rundle on the Trans-Canada Highway between Banff and Canmore provides a classic example of a mountain cut in dipping-layered rocks.

Millions of years ago a collision caused an orogeny, forcing horizontal layers of an ancient ocean crust to be thrust up at an angle of 50–60°.

In strike-slip orogens, such as the San Andreas Fault, restraining bends result in regions of localized crustal shortening and mountain building without a plate-margin-wide orogeny.

Likewise, uplift and erosion related to epeirogenesis (large-scale vertical motions of portions of continents without much associated folding, metamorphism, or deformation)[42] can create local topographic highs.

[44] Before the development of geologic concepts during the 19th century, the presence of marine fossils in mountains was explained in Christian contexts as a result of the Biblical Deluge.

[45] The 13th-century Dominican scholar Albert the Great posited that, as erosion was known to occur, there must be some process whereby new mountains and other land-forms were thrust up, or else there would eventually be no land; he suggested that marine fossils in mountainsides must once have been at the sea-floor.

[47] Elie de Beaumont (1852) used the evocative "Jaws of a Vise" theory to explain orogeny, but was more concerned with the height rather than the implicit structures created by and contained in orogenic belts.

It was, in the context of orogeny, fiercely contested by proponents of vertical movements in the crust, or convection within the asthenosphere or mantle.

[52] Gustav Steinmann (1906) recognised different classes of orogenic belts, including the Alpine type orogenic belt, typified by a flysch and molasse geometry to the sediments; ophiolite sequences, tholeiitic basalts, and a nappe style fold structure.

In terms of recognising orogeny as an event, Leopold von Buch (1855) recognised that orogenies could be placed in time by bracketing between the youngest deformed rock and the oldest undeformed rock, a principle which is still in use today, though commonly investigated by geochronology using radiometric dating.