Geology and Geochronology of Early Precambrian of the Ukrainian Shield
The Early Precambrian of the Ukrainian shield is represented by geological formations older than 2.6 b.y. The Archean formations are established in three big regions of the Ukrainian shield. These regions are tectonic blocks. Each block is characterized by specific petrological and geological features. In each block the grade of metamorphism of the rock is different. The metamorphic rocks are represented by three series and the granites are represented by three complexes. In the lower parts of the section of the series, effusive rocks predominate and in its upper parts metamorphosed sedimentary rocks are predominant. The effusive rocks of acidic and medium composition are characterized by dominating quantities of sodium. Genetically acidic and medium rocks are the products of differentiation of tholeiite-basalt magma. Geochronologically the complexes of granites are characterized in detail. These data were obtained on accessory minerals and correspond to 2.8 b.y. ± 100 m.y. Dates of about 3.0 b.y. were obtained on zircon from metamorphosed effusive rocks by means of U-Th-Pb isotope methods. The data obtained on micas of metamorphosed rocks reflect superimposed processes.