Orogeny

World geologic provinces.jpg of the world (USGS)

{{Legend|#f96|Shield}} {{Legend|#f9c|Platform}} {{Legend|#9fc|Orogen}} {{Legend|#9cf|Basin}} {{Legend|#969|Large igneous province}} {{Legend|#ff9|Extended crust}}

Oceanic crust: {{Legend|#cde|0–20 Ma}} {{Legend|#abc|20–65 Ma}} {{Legend|#89a|>65 Ma}}

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An orogeny is an event that leads to both structural deformation and compositional differentiation of the Earth's lithosphere (crust and uppermost mantle) at convergent plate margins. An orogen or orogenic belt develops when a continental plate crumples and is pushed upwards to form one or more mountain ranges; this involves a series of geological processes collectively called orogenesis.

Orogeny is the primary mechanism by which mountains are built on continents. The word "orogeny" comes from Ancient Greek (ὄρος, óros, lit. 'mountain' + γένεσις, génesis, lit. 'creation, origin'). Although it was used before him, the term was employed by the American geologist G.K. Gilbert in 1890 to describe the process of mountain building as distinguished from epeirogeny.