К ПРОБЛЕМЕ КЛАССИФИКАЦИИ МЕТАМОРФИЧЕСКИХ И МЕТАСОМАТИЧЕСКИХ ПОРОД

Abstract

Numerous contradictions of approaches to classification of metamorphic and metasomatic rocks become clear during preparation of materials for the second edition of «Petrographic Code». The most deep conflicts have come to light in discussions of the following problems: separation of metamorphic, metasomatic and «ultra-metamorphic» formations, as taxons of the same level; distinction of metamorphic and metamorphosed rocks as depended on different intensity of the metamorphism process; a problem of subdivision of metamorphic facies, systematization of conditions and inducements of metamorphism, and unification of classification of the chemical composition of metamorphic rocks. These contradictions arc analyzed critically and some opinions and recommendations are made for their overcoming. For instance, metamorphic and metasomatic rocks must be selected in a separate type of crystalline rocks, whereas the products of granitization (in particular migmatites) be esteemed as another independent type intermediate between metasomatic and magmatic formations. For the conclusion, there arc formulated principles to compose the minimum contradictory classifications of metamorphic, mctasomatic rocks and migmatites, based upon their natural signs and taxons separated to four levels: genetic one (types, subtypes), facial (classes), petrochemical (divisions, subdivisions) and constitutional level (families, species).