Principal stages in geological evolution of Ukrainian shield

Abstract

The first attempt at coordination of the newest geochronological findings with identifiable petrographic complexes within the Ukrainian Shield, here seen as products of geosynclinal evolution and of granitization (in the modern sense), suggests the following characteristic traits of the Precambrian evolution of the earth's crust: an arrest of the upper Archean geosynclinal cycle (the second one of the three) in its initial or early stages; a general non-inversion of geosyncline; a very high geothermal gradient and hence the cardinal role of granitization and the "universality" - involvement of practically all kinds of rocks - of the regional metamorphism. The Shield has behaved as a platfomal entity ever since the end of its last (lower Proterozoic) geosynclinal cycle. The author's historical analysis of the Shield, as distinct from the still current stratigraphic representations, is based among other things on the recognized independence of metamorphic facies from stratigraphic as well as structural boundaries, identifications of formations corresponding to definite stages and zones of the geosynclinal evolution, correlations of geochronological data with petrographic varieties of rocks and with their spatial distribution, examination of migmatites and granitoids from the viewpoints of ultrametamorphism and granitization, proofs of the function of deep fissuring in the character of sedimentation and intrusive activities, and plane analysis of folded structures. Metallogenic analysis of the Shield is facilitated by such identifications and correlations, inasmuch as migrations and accumulations of ore constituents and others were definitely associated with granitization activities. — V. P. Sokoloff