Tectonophysics and structural geology (to the study of the early Precambrian of Ukraine)

• Дата: 2025
• Автор: Gintov, Oleg
• Формат: Стаття
• Мова: Ukrainian
• Опубліковано: S. Subbotin Institute of Geophysics of the NAS of Ukraine 2025
• Теми: Ukrainian Shield; tectonophysics; structural geology; dislocation tectonics; stressmetamorphism
• Онлайн доступ: https://journals.uran.ua/geofizicheskiy/article/view/331592
• Назва журналу: Geofizicheskiy Zhurnal

Tectonophysical findings of the S.I. Subbotin Institute of Geophysics of the NAS of Ukraine and the structural geological research done at the Taras Shevchenko National University of Kyiv are applied here to the problems of studying and mapping the Early Precambrian crystalline basement of the Ukrainian Shield. The positions of both approaches coincide, so they need to be combined, adjusting some differences in terminology. It is shown that when constructing geological and mineral maps of the crystalline basement of the Shield at scales of 1:200 000 and 1:50 000, subhorizontal shear and stress metamorphic processes, shear folding, thrusts and subthrusts were not taken into account as the main ones; no attention was paid to fault zones as shear zones, which are ten or more km wide, have a complex internal structure and special rock fill. The maps did not reflect that most of the crystalline basement of the Shield was completely rebuilt in the Early Proterozoic and the structure which we see now is new, superimposed. Typically, we are dealing with an Early-Proterozoic folding of sub-horizontal pressure and shear that alters and erases previous structures. The Archean rocks within a large part of the Shield have remained only in the form of several small massifs, striations, lenses, and schist inclusions; in the superimposed Early Proterozoic structures, they are usually reoriented in accordance with the direction of the latter. The stratigraphic columns of the Early Precambrian complexes on the published maps are not free from the influence of the stratigene-metamorphogenic approach, according to which the primary Archean-Early Proterozoic sedimentary-volcanogenic rocks that comprise the horizontal layers have been folded into synclines and anticlines with subhorizontal joints and their relative age can be determined by studying such folds and using isotope-geochronological studies as auxiliary or secondary data. In fact, as established by the modern tectonophysical and structural geological studies, the Archean structural plan of most areas of the Ukrainian Shield has been restructured several times since the Neoarchean, and the vertical crustal sections observed in the outcrops are monoclines with a sub-vertically layered structure. The Early Proterozoic shear fold formed in such conditions was subvertically articulated. A model and examples of such folds are presented.