Principles of metamorphic petrology \ Принципы метаморфической петрологии

Metamorphism refers lo Ihe inineni logical and structural alteration of rock к in Karth's crust, and excludes alteration at or just beneath ihe surface, such as weathering and early diagencsis. However, diagenetic changes grade into mctamorphic changes in burial meuimorphism. In face* metamor-phism may occur in several geological environments, because assemblages react to changes in temperature (T), pressure (iJ) and activities of mobile chemical components, regardless ol the geological processes responsible for the changes. For example, identical or very similar assemblages can be formed by (1) deuleric alteration in an igneous intrusion 12) wall-rock alteration around a hydro! hernia) orebody. (3) low-tempe rat lire alteration around an igneous intrusion, (4) burial metamorphism of sedimentary/volcanic successions and (5) alteration, both local and regional, in geothermal areas (Vernon. 1976f.