On the so-called “leukogranulite formation” and “greenlevada suite” of Early Precambrian of the Ukrainian Shield

• Дата: 2018
• Автори: Ponomarenko, O., Gintov, O., Stepanyuk, L.
• Формат: Стаття
• Мова: rus
• Опубліковано: Subbotin Institute of Geophysics of the NAS of Ukraine 2018
• Теми: the Ukrainian Shield; Middle Bug area; Lower Archean; Proterozoic; leucogranulites; metasomatites; fault zones; tectonophysics; radiogeochronology; stratigraphy
• Онлайн доступ: https://journals.uran.ua/geofizicheskiy/article/view/147474
• Назва журналу: Geofizicheskiy Zhurnal

It has been shown using as an example the geological structure of the Precambrian basement of the Middle Bug area (the Ukrainian Shield) that the chronostratigraphic scheme of the Lower Archean needs to be modified, in particular, greenlevada suite of the Dniester-Bug series represented by supercrustal leucogranulite rock formation sho-uld be included. It has been found that leucogranulite formation of the Bug area are rocks (granitized biotite and garnet-biotite gneisses) which belong to formation-gene-tic type of quartz-feldspar metasomatites, particularly, to structural-formational association of metasomatites from regional fault zones. According to the data of geological, geochemical, tectonophysical, radioisotopic studies of the similar rocks in the exposures of the middle stream of the river South Bug, it has been proved that they were formed around 2.03 Ga ago as a result of diaftoresis of rocks of the Archean basement and their granulitic appearance as well as subvertical occurrence are related to dyna-mometamorphic including shear processes. Methodic problems of the studies of the age relations of the Catarchean rock complexes are under discussion. The well-known geological cross-section of Khoshchuvato-Zavalye site of the Middle Bug area has been considered and it has been shown that the stratigraphic method based on the principle of sequence of stratifying of supercrustal rocks is impossible to be effectively used in such complexes because of their strong tectonic and intrusive-metasomatic reprocessing, practical impossibility of their initial bedding to be found. The best way under these conditions is to be supported by more objective petrostructural, microstruc-tural, petrochemical, including radioisotopic and geophysical data.