A TENTATIVE CLASSIFICATION OF THE TYPES OF METAMORPHISM

Metamorphism is one of the main geological processes occurring in the evolution of the earth’s crust. According to the recent development of metamorphic geology, Lyell’s definition of metamorphism may be emphasized as those endogenous processes within the crust mainly initiated by the interaction between the upper mantle and the crust, the heat flow and the accompanying deformation of which cause the rock transformation essentially in a solid medium, but while the temperature rise exceeds certain limit, then migmatization and anatexis will be followed with or without the participation of some ichor solutions coming from the depth, and finally a magmatic regime is reached where different kinds of granite can be produced. In this sense, the metamorphim may be considered as the reconciliation of the conflicts between the neptunists and the plutonists within crustal domain.Metamorphism, magmatism and stress deformation are considered as three separated geological processes independent from each other.They are all governed by some constraints which are more intrinsic in nature in the course of the crustal evolution. However, the appearence of their associations is not uniquely represented, as the tradition view holds, but is rather controlled by the different paths of the crustal evolution, the ultimate cause of which is yet to be unravelled, though the theory of plate tectonics has given a reasonable interpretation in this field. In dealing with the classification of the types of metamorphism, the complete process evolved during and subsequent to metamorphism should be taken into consideration, which includes the initial condition of the metamorphism, comprising both the nature of original rock associations and their tectonic settings; the physico-chemical conditions governing; the metamorphism and finally some subsequent petrological events which are not related to metamorphism directly, but are in the Same Concordent tectohic pattern during the evolving period. Accordingly, the following tentative classification of the types of metamorphism are proposed, each compounded with a brief description on original rock associations, tectonic settings, characters of metamorphism, migmatization granitic magmatism. 1. Regional dynamo metamorphism: chiefly due to stress action; （a） Slate or phyllite metamorphism （regional dynamometamorphism, sensu stricto） 2. Burial metamorphism: due to burial or sinking of the sediments, sometimes nappe structures are also involved; （a） Zeolite facies metamorphism （b） High pressure regional metamorphism （glaucophanelawsonite facies metamorphism） 3. Medium pressure regional metamorphism; 4. Low pressure regional metamorphism; 5. High temperature regional metamorphism（granulite metamorphism）; 6. Contact metamorphism; （a） Pyrometamorphism （b） Contact metamorphism related to batholithic granitic magmatism （c） Contact metamorphism related to andesitic magmatism 7. Cataclastic metamorphism （dynamometamorphism）; 8. Ocean floor metamorphism: some ancient deep sea greenstone series and ophiolite suites may be included; 9. Impact matamorphism（shock metamorphism）; As to the terms such as autometamorphism and hydrothermal metamorphism, they are generally considered as later stages of some magmatic processes, so they are not represented as the main types of metamorphism in this classification.