Abstract:
The East Sayan fold system, including northeastern Tuva, is confined to the southwest rim of the Siberian craton and acquired its present structure chiefly in the early Caledonian (Salairian) epoch. The most interesting suite in the Precambrian section of northeastern Tuva is the Shutkhulay, because it is the oldest. However, virtually nothing is known about its age, composition or metamorphism. We studied in detail garnetiferous high-alumina varieties with cordierite and sillimanite as the most informative for determining the thermodynamic regime of their formation. Our calculations of the thermodynamic regime and natural mineral-forming reactions, taking into account the chemical composition of the minerals in the high-alumina rocks, indicate that regional metamorphism of the Precambrian strata of the Shutkhulay suite was progressive and occurred under conditions transitional from the top of the amphibolite facies to the granulite.