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Orogeny refers to forces and events leading to a large structural deformation of the Earth's lithosphere (crust and uppermost mantle) due to the interaction between tectonic plates. Orogens or orogenic belts develop when a continental plate is crumpled and is pushed upwards to form mountain ranges, and involve a great range of geological processes collectively called orogenesis. The word "orogeny" comes from the Greek (''oros'' for "mountain" plus ''genesis'' for "creation" or "origin"), and it is the primary mechanism by which mountains are built on continents. Geomorphology is the study of landforms and the processes that shape them. ==Physiography== Formation of an orogen is accomplished in part by the tectonic processes of subduction, where a continent rides forcefully over an oceanic plate (noncollisional orogens), or convergence of two or more continents (collisional orogens).〔 〕 Orogeny usually produces long arcuate (from ''arcuare'', to bend like a bow) structures, known as ''orogenic belts''. Generally, orogenic belts consist of long parallel strips of rock exhibiting similar characteristics along the length of the belt. Orogenic belts are associated with subduction zones, which consume crust, produce volcanoes, and build island arcs. The arcuate structure is attributed to the rigidity of the descending plate, and island arc cusps are related to tears in the descending lithosphere.〔 〕 These island arcs may be added to a continent during an orogenic event. The processes of orogeny can take tens of millions of years and build mountains from plains or the ocean floor. The topographic height of orogenic mountains is related to the principle of isostasy, that is, a balance of the downward gravitational force upon an upthrust mountain range (composed of light, continental crust material) and the buoyant upward forces exerted by the dense underlying mantle. Frequently, rock formations that undergo orogeny are severely deformed and undergo metamorphism. During orogeny, deeply buried rocks may be pushed to the surface. Sea bottom and near shore material may cover some or all of the orogenic area. If the orogeny is due to two continents colliding, the resulting mountains can be very high (see Himalayas). An orogenic event may be studied as: (a) a tectonic structural event, (b) as a geographical event, and (c) a chronological event. Orogenic events: (a) cause distinctive structural phenomena related to tectonic activity, (b) affect rocks and crust in particular regions, and (c) happen within a specific period. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Orogeny」の詳細全文を読む スポンサード リンク
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