Abstract
According to the results of U-Pb geochronological studies, it was established that the amphibolites of the Novo-Pavlivka greenstone structure of the Middle Dnieper megablock formad in Archean. They are broken through by cataclased low-alkaline granites aged 2784 ± 45 Ma. Zircon from them has undergone significant metamorphic transformation. In the internal structure of the zircon, it is observed that the peripheral parts are illuminated, non-zonal, and in the central parts – unchanged zonal zircon is preserved. The isotopic age values for different uranium-lead ratios are characterized by a significant direct discordance, which indicates a disturbance of U-Pb zircon system. The isochron constructed from the uranium-lead ratios of this zircon has two intersections with concordia. The upper section corresponds to the isotopic age — 2784 ± 45 Ma, and the lower one — 384 ± 273 Ma. The obtained data indicate a violation of the U-Pb system of zircon, which arose as a result of dynamometamorphism. Zircon dating is probably underestimated and does not correspond to the age of formation of the investigated plagiogranites. The tectonic processes associated with this dynamometamorphism probably took place in the Paleoproterozoic during the general collision of Archean blocks on the Ukrainian Shield. The high degree of alteration of zircon indicates a significant influence of fluids during dynamometamorphism. As a result, ore elements, including gold, could be mobilized and transported from the ultrabasic-basic complexes of the Sura suite, which underwent dynamometamorphism.
Publisher
National Academy of Sciences of Ukraine (Co. LTD Ukrinformnauka) (Publications)
Reference6 articles.
1. 1. Artemenko, G.V., Samborska, I.A., Shvaika, I.A., Gogolev, K.I. and Dovbush, T.I. (2018). Stages of Early Proterozoic collisional granitoids magmatism and metamorphism in the Azov and Middle-Dnieper megablocks of the Ukrainian shield. Mineral. Journ. (Ukraine), 40, No. 2, P. 45-62.https://doi.org/10.15407/mineraljournal.40.02.045 [in Russian].
2. 2. Zakharov, V.V. (1998). Geological, structure, minerals and geoecological situation of the Krivyi Rig iron ore region. 1 : 200000 (Geological study of areas- 200) sheets M-36-XXXIV, L-36-IV, produced in 1991-1998. (in 3 books). Krivyi Rig [in Russian].
3. 3. Bogatikova, O.A., Gonshakova, V.I. (Eds). (1983). Igneous rocks: Classification, nomenclature, petrography. Nauka, Moscow. Part 1. 365 p. [in Russian].
4. 4. Ludwig, K.R. (1991). ISOPLOT for MS-DOS. A Plotting and Regression Program for Radiogenic-Isotope data, Berkeley Geochronology Center: revision of U.S. Geolю Survey Open-File Rept. No. 88-557.
5. 5. Ludwig, K.R. (1993). PbDAT Computer Program for Processing Pb-U-Th Isotope Data. Version 1.24, Berkeley Geochronology Center: revision of U.S. Geol. Survey Open-File Rept. No. 88-542.