Geotectonic studies of the basement of the Ukranian shield based on geologic-formation approach: key findings

Purpose. To present the summary of findings of the geotectonic analysis of the basement of the Ukrainian Shield (US) and to give grounds for the specific conditions of its formation in the Early Precambrian. Methodology. Conducting analysis using the latest results of the of morphoparagenetic geological-formational studies and concepts as to the layer-block structure of the region. Results. Main result of the geotectonic research consisted in compiling the tectonic map of the Ukrainian shield, scales 1:2 500 000 and 1:2 000 000, as well as in substantiating a number of important conclusions on local geotectonic structure and development of the region: a) All main types of Early Precambrian Shields stratogenic metamorphic complexes are represented on the US: granulite-gneissic, amphibolite-gneissic, greenstone, iron-siliceous-schistose, gneiss-schistose. The complexes clearly differ by their geoformational content, pointing out the directed geoevolutional change in conditions that led to these complexes formation; b) In the basement of the US one can isolate six megablocks, in which the stratometamorphic complexes, either themselves, or along with the ultrametamorphic formations, make up the structural stage; c) Based on the combination of structural stages, five types of megablocks can be isolated on the US: granulite, granulite-diaphtoritic, granulite-amphibiotic, amphibolite-greenstone, granite-gneiss-schistose; d) The analysis of the spread of the staratometamorphic complexes within the block structure of the US gives grounds to isolate two geotectonic periods in its development, or megachrons – Eogey and Protogey. Each megachron can be subdivided into early and late stages, or geochrons, which differ by formation of stratogenic complexes, different in their geoformaitonal content; e) A brief geoevolutionary characteristic and the age borders of these stages are provided. Originality. The result of the conducted research is a generally complete concept if the structure-material and geotectonic evolution of the US in Early Precambrian. Practical significance.  The obtained results can be used in local works and regional mapping. Based on them, it's possible to conduct more detailed paleo-tectonic and the accompanying paleo-geographic fascial-formational reconstructions of separate phases and stages of formation of the  structures of mega-blocks and the US in general, as well as to develop their general geodynamic (geoevolutionary) history.