Metasomatism

Japanese: 交代作用 - こうたいさよう（英語表記）metasomatism

A phenomenon that generally occurs in metamorphism, in which the overall chemical composition of the parent rock changes due to the introduction or release of substances such as volatile components or solutions from the outside, and the original substances are replaced by minerals of different chemical composition through chemical reactions. Rocks formed by metasomatism have a very different chemical composition from the original rock due to the movement of components, but the original rock texture may still remain [Naumann: 1826, Lindgren: 1912]. In the case of mineral deposit formation, it refers to the process in which minerals or rocks are replaced by minerals or rocks of different chemical composition while leaving their original shapes almost intact [Katayama et al.: 1970]. Metasomatism is generally accompanied by metamorphism under high temperature and pressure conditions, such as contact metamorphism and deep metamorphism. The process of metasomatism does not require the presence of melts, but the entire system must be open [Suzuki: 1994].

Substitution

(1) The process by which one substance is replaced by another. The process by which a mineral or rock is replaced by a mineral or rock of a different chemical composition while leaving most of its shape intact. (2) Used synonymously with metasomatism (3.1.1(4)).

Source: Asakura Publishing Dictionary of Petrology Information

Japanese:

変成作用で一般に行われる現象で，岩石の原岩の総化学組成が外部から揮発成分や溶液などの物質が導入あるいは放出されて変化し，本来あった物質が化学反応によって別の異なった化学組成の鉱物で置換される過程．交代作用で形成された岩石は，成分の移動によって元の岩石の化学組成が非常に変化するが，もともとの岩石の組織が残っていることもある［Naumann : 1826, Lindgren : 1912］．鉱床生成の場合には鉱物または岩体の形をほぼ残して，化学組成の異なる鉱物または岩石に置換される作用をいう［片山ほか : 1970］．交代作用は一般に接触変成作用や深部における変成作用など高い温度や圧力の条件下の変成作用に伴われる．交代作用の起こる過程では溶融体などの存在は必要ないが，全体の系は開放されている必要がある［鈴木 : 1994］．