pdf № 346, October

DOI: 10.19110/geov.2023.10.1

The structural features of the rocks of the Precambrian section of the Subpolar (upper reaches of the Kozhim River) and Polar Urals (Kharbey River basin) have been studied. We revealed that the structural appearance of the formations under consideration resulted from several stages of deformation. The Precambrian of these regions is characterized by deformations and accompanying metamorphic transformations of rocks in the Early Proterozoic, associated with orogenic processes resulting from the unification of Volga-Uralia and Sarmatia and later with the development of the timanides and uralides. We found markers of an earlier stage of structural-metamorphic transformation of rocks (possibly Late Archean) in the Polar Urals.

Keywords: Subpolar and Polar Urals, Precambrian, structural analysis, stage of deformation.

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DOI: 10.19110/geov.2023.10.2

The Pechora Basin is the largest tectonic structure of the Pechora Plate. It is located between the Timan and the Cis-Ural Foredeep. The Upper Precambrian sedimentary-metamorphic and igneous rocks of the basement are completely overlain by a sedimentary cover, therefore, the geological structure of the basement is known only on the basis of geophysical data and core samples from boreholes up to 5 km deep. The basement has a heterogeneous structure. It includes complexes of the Late Precambrian passive margin of the East European continent, which compose the Timan megablock (Izhma zone with Timan adjoining from the southwest) and formations formed in an active margin geodynamic setting combined into the Bolshezemel megablock (Pechora and Bolshezemel zones). The boundary between megablocks is the Pripechora fault (suture) zone. The age of igneous rocks of the basement is debatable; therefore, U-Pb (SIMS) studies of single zircon grains are undertaken to specify it. The article presents petrogeochemical data and U-Pb (SIMS, SHRIMP-RG) ages of zircon grains from plutonic rocks of the Pechora zone belonging to the Bolshezemel megablock drilled by two boreholes at depths of ~ 4.5 km. The obtained results indicated two episodes of island-arc magmatism. The first took place at the end of the Riphean, and the second was confined to the Early–Late Vendian boundary. The age of gabbrodiorites from the 1-Severny Savinobor borehole, interpreted as early island-arc rocks, is 673 ± 7 Ma. Late island-arc plagiogranites from the 1-Novaya borehole yield the age of 564 ± 5 Ma and precede the orogenic granitoids of the Pripechora fault zone which are dated (U-Pb) to 555—544 Ma.

Keywords: Pechora Basin, Pechora zone, Neoproterozoic, basement, gabbrodiorites, plagiogranites, zircon, U-Pb age.

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DOI: 10.19110/geov.2023.10.3

A small dike of unknown age was found on the territory of the Kanin-Timan region within the Middle Timan along the Lunvozh river. Our studies revealed that the rocks, composing this intrusive body, corresponded to basaltic andesites according to the content of the main rock-forming elements. They were almost completely recrystallized and composed of chlorite (30—40 %), carbonates (25—40 %), albite (10—15 %), quartz (10—15 %), muscovite (5—8 %) and plagioclase (less than 1 %). Accessory minerals were represented by apatite, monazite and rutile. Ore minerals included pyrite, chalcopyrite, and cobaltine. According to the mineral composition and petrochemical characteristics, the rocks composing the dike body along the Lunvozh river, differed from the basites of the Middle Riphean Middle Timan and Devonian Kanin-Timan complexes identified in the Kanin-Timan region.

Keywords: metabasites, dike body, isotope analysis of carbon and oxygen, Lunvozh river, Middle Timan.

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DOI: 10.19110/geov.2023.10.4

A sample of Domanik shale from a stratotype section along the river Chut (Ukhta District, Komi Republic, Russia) was affected to temperatures of 250—375 °C in an autoclave in the presence of water. The composition and yield of the resulting hydrocarbon gases was studied by gas chromatography. The yield of all C₁—C₅ hydrocarbons grew exponentially with increasing temperature in the autoclave. The total yield of gaseous hydrocarbons C₁—C₅ at 375 °C was 71 mg/g Corg and reached 18 mg/g C_org for methane. The increasing temperature in the autoclave resulted in decreasing ratio of methane/C₂₊ gases, which reflected a changing mechanism of methane formation at the corresponding stage of the thermal evolution of the Domanik organic matter.

Keywords: domanik shale, hydrocarbon gases, hydrous pyrolysis in an autoclave, organic matter.

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DOI: 10.19110/geov.2023.10.5

The Bolshezemelskaya tundra is one of the least studied and poorly mapped territories of the European North-East of Russia. The availability of the ArcticDEM digital elevation model with a high spatial resolution allowed conducting a comprehensive joint analysis of digital, geomorphological and geological data.

The results of using the ArcticDEM global digital relief model for geological and geomorphological studies of the Seyda River basin (eastern Bolshezemelskaya tundra) in its middle and lower reaches are presented.

An irregular triangulation network TIN covering the Seyda River valley was constructed, and the main geomorphometric parameters of the relief were calculated: hypsometric characteristics, surface inclination angles and slope exposures. Based on the obtained morphometric indicators of the relief and the textural and structural characteristics of Quaternary sediments, the following types of relief were identified: accumulative glacial, erosion-accumulative water-glacial and erosion-accumulative alluvial types of relief. A geological and geomorphological diagram of the Seyda River valley was been constructed and the main morphogenetic features of the relief during its formation were identified.

Keywords: digital elevation model, ArcticDEM, geomorphological zoning, morphometric analysis.

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DOI: 10.19110/geov.2023.10.6

The article examines patterns of spatial distribution of ¹³⁷Cs and natural radionuclides ²²⁶Ra, ²³²Th, ⁴⁰K in the upper (0—5 cm) layer of soils in the main functional zones of the city of Polyarnye Zori. The analysis of the general gamma activity of the territory, using RS-700 mobile gamma spectrometric complex, showed, three local anomalies of increased gamma radiation, which were confined to high-rise buildings within the city. In undisturbed peat soils in the area of the Kola Nuclear Power Plant and in the area of urban forests and parks, the maximum specific activity of technogenic ¹³⁷Cs was 29.5 and 28.8 Bq/kg, respectively. In other functional zones of the city, the activity of ¹³⁷Cs was 5 times less. According to the results of the correlation analysis, the technogenic ¹³⁷Cs has a moderate relationship (on the Chaddock scale) with the 45 and 500 µm fraction. ²³²Th has a high affinity with ²²⁶Ra, and ⁴⁰K with ²³²Th, which are statistically significant results when taking P-Value into account. It can be assumed that natural radionuclides ²³²Th, ⁴⁰K, ²²⁶Ra have a moderate association with the 1 mm fraction due to the presence of particles of this size in the upper soil layer. There is a moderate relationship between ²³²Th and ⁴⁰K.

Keywords: specific radioactivity, urban soils, ¹³⁷Cs, ⁴⁰K, ²²⁶Ra, ²³²Th, Polyarnyye Zori, Murmansk region.

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