Periodization and specific features of deep processes in Precambrian by example of the Ukrainian shield
Journal Title: Геофизический журнал - Year 2017, Vol 39, Issue 6
Abstract
Thorough information on geological structure of the Ukrainian shield (USh) allows to verify opinions existing nowadays that plume and plate tectonic activities are possible only after conclusive formation of sublithospheric mantle 2,8—2,55 Ga and plume episodes of Precambrian occurred 2,75—2,7, 2,45—2,4, 1,9, 1.8—1,75, 1,65 Ga ago. It can be proved nowadays that formation of the crust occurred before 4.0 Ga and plume events result in later transformation of not only crust but also of mantle. Isotope dating of the USh allows allocating of plume episodes in close-range time. Nevertheless these limits for the USh in many cases have connection with geological processes, because not detrite zircons are dated but those ones included in rocks. Individual episodes are united into lasting plume events (activizations) up to 3,2, 3,2—2,8, 2,7—2,3, 2,3—1,65 Ga. Special features of the structure of granite-greenstone area of the Middle Dnieper megablock of the USh support the opinion that before 2,7 Ga thick sub-continental lithosphere consisted of refractory peridotite did not exist. Crystallizable layer consists of relatively low-melt minerals and is enriched by basaltoid component. The thickness of crystallized layer reduces up to 100 and 50 km in case of addition of reheated deep matter and increases during crystallization up to 150—200 km. Asthenosphere compulsory contains the melt diluted by silicate-aqueous-carbonate fluide. After 2,7 Ga subdivision of the area into two big blocks occurred. At the mark of the Archean and Proterozoic (2,5 Ga ago) the territory of Ukraine was subdivided into blocks and territories which spatially were drawn towards suture zones. The composition of the terrains allows supposing that at the mark of the Archean and Proterozoic exarticulation of tectonic units where plume processes went in different ways occurred. The following plume event (2,3—2,65 Ga ago) was manifested as a stage of transformation of mantle and crust on all the cratons. In the structure of the USh obvious features of plate tectonic processes have been found. Movements maximal by amplitude occurred 2,0—1,8 Ga ago. During the process of this plume event abrupt change of composition of fluids and melts removed from the mantle occur. Granitization takes place with participation of aqueous chloride-potassium fluids. After granitization active dry carbonate-fluoride-sodium fluids became active. Removal of melts, fluids occurs by small portions and the regime of pulsating plume considerably specifies the composition of magmatic rocks and hydrothermal solutions.
Authors and Affiliations
O. V. Usenko
Keywords
Related Articles
- EP ID EP243660
- DOI 10.24028/gzh.0203-3100.v39i6.2017.116366
- Views 85
- Downloads 0
Few words about Boris Paton
Few words about Boris Paton
The system of early warning on strong sub-crustal earthquakes of the Vrancea zone
The article is devoted to the issue of seismological monitoring and automatic warning of the personnel of potentially hazardous manufactures on the approaching of seismic threat and warning the population, in order to ad...
Study of the piezoelectric sensor KD-35 properties on the calibration device by the method of external pulse and on a real Earth track
Microseismic monitoring of rock mass, such as mines, will provide data about condition of mass on the borders of waste areas at different levels of implementation of mining. The main problems of monitoring are the inform...
Software system for automated data interpretation of potential fields (GMT-Auto)
Principles of operation have been set out for a program complex of the potential fields automated interpretation (GMT-Auto) aimed at: 1) computer input automation for images of geologic-geophysical maps with subsequent t...
Two approaches to the problem of ray seismic tomography
Approximation of nonlinear geophysical medium as a linear one substantiates a transition to geometrical seismics based on geometric optics. Conditions, necessary and sufficient for application of geometrical optics bring...