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the processes of the formation of magma, its subsequent development, displacement, interaction with solid rocks, and solidification.
As one of the most important manifestations of deep-seated activity of the earth, magmatism is directly or indirectly bound up with the development of the earth, its thermal history, and its tectonic evolution. When the nature of tectonics changes there is also a change in the type of magmatism; depending on geological history and confinement to some particular structure of the earth’s crust magmatism is subdivided into geosynclinal, platform, oceanic magmatism, and magmatism of activization areas. Depending on the depth of manifestation (conditions of magma solidification) magmatism is divided into abyssal, hypabyssal, subvolcanic, and surface magmatism. (The last is known as volcanism.) By composition the breakdown is ultrabasic, basic, acid, and alkali. Some experts believe that magmatic processes are especially intensive in the geosynclinal period of the development of folded areas and that certain forms of the manifestation of magmatism are associated with definite stages in the development of a geosyncline. In the modern geological epoch magmatism is especially highly developed in the Pacific geosynclinal belt, the midocean ridges, the rift zones of Africa and the Mediterranean region, and elsewhere. The formation of many different deposits of minerals is associated with magmatism.