Abstract
Precambrian rock types consist of metasediments and metavolcanics and occur generally throughout the entire Russian platform and adjacent Ukrainian crystalline shield. Rocks of different ages and belonging to different structural stages and diastrophic periods show different degrees of crystallization. From Archean rocks to Proterozoic rocks, the degree of recrystallization decreases greatly. Reliable correlation criteria are the degree of crystallization and the similarity of rocks, of the same age, which have been subject to identical tectonic conditions. The petrography of the ortho- and pararocks corroborates the hypothesis of granite forming from partially molten, ancient, sedimentary rocks subsequently altered by various metasomatic processes. Study of the mineral composition of gabbros and pyroxene paragneisses indicates the actual manifestations of basic magma were effective as early as Archean and have been active to the present. R.M. Hutchinson
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