pdf № 359, November

DOI: 10.19110/geov.2024.11.1

A lot of buried valleys exist on the territory of the northwestern East European Plain. They are deeply cut in the pre-Quaternary rocks. The buried valleys genesis is a long-standing question of the Quaternary geology of the northwestern Russia. By now, geological data have been accumulated to solve this problem. The geological structure of the buried valleys was detailed on the basis of unpublished reports and published materials on geology of buried valleys of Saint-Petersburg, Leningrad, Pskov, Novgorod and Kaliningrad regions as well as adjacent regions of Estonia, Latvia, Lithuania and Belarus. Most of the data do not exclusively testify to river-erosion genesis of the valleys. Modern data also suggest that some of the buried valleys of the northwestern Russia are tunnel valleys and were formed by subglacial meltwater erosion as well as buried valleys of neighboring regions.

Keywords: buried valleys, pre-Quaternary surface, pre-glacial river network, subglacial erosion, tunnel valleys, Scandinavian ice sheet, north-west of the East-European Plain

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DOI: 10.19110/geov.2024.11.2

The results of local U-Pb (SIMS) zircon analysis indicate that plutonic rocks drilled by five boreholes in the Izhma zone of the Timan megablock of the Pechora Basin basement were not intruded simultaneously in the Late Precambrian. The first episode of magmatic activity took place at c. 600 Ma (at the Riphean — Vendian boundary), while the second one is confined to the Late Vendian. The ages of the granites from the 1-Nizhnyaya Omra and 1-Prilukskaya boreholes are 602 ± 2 and 593 ± 14 Ma, respectively. The granites from the 11-Malaya Pera and 1-South Djer boreholes and diorites from the 21-Palyu borehole are 557—536 Ma old, being well correlated to the 555—544 Ma old orogenic granitoids of the Pripechora fault zone (the supposed suture of the Timanides orogen).

Keywords: Pechora basin, Izhma zone, basement, granites, diorites, zircon, U-Pb age

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DOI: 10.19110/geov.2024.11.3

A mineralogical and geochemical study of vesuvianite from mineral aggregates sampled in the Zelentsovskaya, Nikolaje-Maximilianovskaya, Akhmatovskaya and Shishimskaya mines located at the outer contact of the Kusa-Kopan intrusion of the Southern Urals was carried out. Vesuvianite from the silicate-carbonate rock (Zelentsovskaya mine) is significantly enriched in Fe, V, Cr, Y, Zr, Th, Sn, and Cl, and the REE distribution spectrum it is close to that for garnets from the same rocks. Vesuvianite from calcite-garnet vein in chlorite schist (Nikolaje-Maximilianovskaya mine) is enriched in U, and REE distribution spectra there are significantly differentiated, which is explained by the removal of incompatible elements. Vesuvianite from rodingites (Akhmatovskaya mine) is enriched in Mn, Ni, Zn, Sr, Nb and volatile components (F and Cl), and the REE distribution spectra are conformal to each other, which testifies to a stable geochemical equilibrium in the rock. Vesuvianite from the skarn (Shishimskaya mine) is in paragenesis with garnet, so it is significantly enriched in Al, LREE and water, and depleted in impurity elements. The content of trace and rare-earth elements in all vesuvianites shows signs of contact metasomatism: the peculiarities of their composition depend on the mineral paragenesis and the influence of the frame rocks — gabbroids of the Kusa-Kopan intrusive complex.

Keywords: vesuvianite, silicate-carbonate rocks, rodingite, skarn, Kusa-Kopan complex, Southern Urals, trace and rare-earth elements, REE, SIMS method

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DOI: 10.19110/geov.2024.11.4

Nanostructured 3D matrices based on monodisperse spherical silica particles are currently of considerable interest due to the prospects for their widespread use in the synthesis of new nanocomposite materials. At the same time, one of the main problems hindering their large-scale synthesis is associated with the unstable behavior of tetraethoxysilane (TEOS) during its hydrolysis and, as a result, poor reproducibility of the sizes of the formed silica particles under given conditions. In this work, based on the study of the elemental composition of impurities in silica opal matrices obtained from tetraethoxysilane from various manufacturers, we continued to study factors affecting the size of the formed particles.

To solve this problem, samples of supramolecular structures obtained from TEOS from various manufacturers were examined by the ICP-MS method for the content of impurity elements in them. It is shown that the content of elements in the initial TEOS correlates with deviations in the size of the formed silica particles. The experiments carried out on the synthesis of spherical particles with the introduction of additives of a number of previously defined elements confirm the obtained dependence. Moreover, it was found that the presence of certain impurity elements in the system increased the monodispersity of the sizes of the formed silica particles, which was a fundamentally important step to solve the problem of obtaining silica particles of a given size with high reproducibility of results. The obtained results are important for understanding the features of the formation of supramolecular structures of silica in nature.

Keywords: monodisperse spherical silica particles, supramolecular structures, physicochemical methods of analysis

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