~(40)Ar/~(39)Ar Age of the Polyfacies Metamorphism of Sedimentary—Volcanogenic Sequences of Tunka Goltsy, Eastern Sayan

摘要

During many dozens of years, metamorphic grade served as the main criterion in estimating the age of paleontologically barren metamorphic sequences. Rocks metamorphosed under a grade higher than greenschist facies were usually considered as Pre-cambrian in age. Correspondingly, the same criterion was applied in tectonic delineation, being the basis for distinguishing Precambrian basement inliers, median massifs, and blocks. In the 1960s—1970s, the approach to interpretation of metamorphic heterogeneity began to change.