THE ISOCHEMICAL NATURE OF THE CONTACT METAMORPHISM OF HIGH-ALUMINA METAPELITES IN THE AYAKHTA GRANITOID MASSIF, YENISEI RIDGE

Abstract

Study of graphite-bearing ferriferous high-alumina hornfelses nearby an intrusive body of granitoids were carried out to investigate the matter behavior and elucidate the conditions under which mineral assemblages of thermal metamorphism developed. Geothermobarometric study and analysis of mineral equilibria permitted estimation of the P-T-XH2O-conditions of contact metamorphism. It is concluded that the formation of chloritoid nontypical of thermal metamorphism and the stability of rare parageneses (chloritoid + biotite, chloritoid + biotite+ + andalusite) in contacting aureoles are the result of a rare combination of elevated (for thermal metamorphism) pressures (≥3 kbar) with specific rocks rich in both aluminum and iron. Special petrochemical studies have shown that metapelites underwent isochemical transformations and the evolution of their chemical composition under contact metamorphism depended on the initial PT-conditions.