Thesis for a Candidate Degree in Geology: Speciality 04.00.01 – general and regional geology. – Taras Shevchenko National University of Kyiv, Ministry of Education and Science of Ukraine, Kyiv, 2021.
The dissertation is devoted to a comprehensive study of the fenite halo of the Proskurov massif (PM) of alkaline rocks in comparison with the Chernigovka carbonatite massif (ChCM). The geological position, mineralogical, petrographic and geochemical features of the rocks, the content of trace elements and the Sr isotopic composition of apatites from these rocks have been investigated.
Changes in the material composition of PM fenites are manifested at the level of the mineral and chemical composition. At the level of mineral composition, the fenitization process consists in the disappearance of relict mineral associations of the original PM rocks (granitoids and garnet-biotite gneisses) and the formation of new ones in the final fenitization products. The behavior of chemical elements in the process of fenitization of the PM frame rocks is manifested in the convergence of the compositions of the end products of fenitization. This is best manifested in the behavior of alkalis (Na2O+K2O) and P2O5. A similar picture is observed for fenitized rocks and fenites of the CCM. Moreover, the contents of these components are close for the two massifs, which is reflected in the quantitative ratios of rock-forming minerals. At the same time, the content of trace elements (especially indicator for alkaline rocks - REE, Nb, Sr, Zr, etc.) for fenites of the two massifs differ. Thus, the content of REE, Nb in PM fenites is an order of magnitude lower than in ChCM fenites.
For the first time, regular changes in the impurity composition of apatites from the rocks of its fenite halo were established for the PM. These patterns testify to the geochemical zoning manifested at the mineral level, which corresponds to the distinguished metasomatic columns. For ChCM, such studies were carried out earlier, and in this work they were confirmed. In addition to the established zoning, the convergence of the compositions of the newly formed generations of apatite was also traced.
Determination of the Sr isotopic composition of apatites from all identified rock types of both massifs indicates a similar level of their depth, which additionally indicates the similarity of the conditions for the formation of alkaline magmas, from which the massifs were formed, and, accordingly, the fluids that caused fenitization.
The results of the dissertation work can be used to search for massifs and manifestations of alkaline rocks and carbonatites on the Ukrainian Shield and within other closed areas. The obtained analytical data can be used in future studies to assess the composition of the fluid that led to fenitization, the degree of its relationship with alkaline magmas, and develop modern ideas about the latter.
