No 3 (2024): Науки о Земле

The study on lherzolites of the North Kraka massif, which is part of the largest (more than 900 km2) lherzolite allochthon (composed of island-arc and oceanic complexes thrusted from the eastern slope of the Urals onto bathyal and shelf deposits of the passive continental margin of the East European Platform), contains REE ID-ICP-MS, ⁸⁶Sr/⁸⁷Sr and ¹⁴⁷Sm-¹⁴³Nd ID-TIMS results indicating melting of the already depleted protolith, which can be identified as a mantle source with parameters similar to MORB. Comparison of the currently available geochemical and geochronological signatures of the Kraka massifs with the similar materials from Central and Western Europe allows to correlate the structures of Timanides with Cadomids formed as a result of this folding phase, which ultimately, based on global reconstructions of the continents for the end of the Proterozoic, authorize the hypothesis of the Cadomian orogen existence on the periphery of Gondwana.

The paper discusses mineral and structural properties of paragneisses of the Nyartinskiy complex and the Mankhobeyskaya suite. The PT-parameters of mineral equilibria of the second and third metamorphism stages have been estimated using the computer programs by the classical and multi-equilibrium mineral thermobarometry methods. By the microstructural parameters, the study rocks undergo three independent tectonic-metamorphic stages. The first stage is acknowledged by the presence of strongly compact and isoclinal folds in the paragenesis with first-generation foliation and by relict minerals that are absent in the overlying (Upper Riphaean) sediments. The second stage corresponds to the progressive metamorphism with principles of the epidote-amphibolite facies (metamorphism peak T=606-527 °C, P=8.8-7.9 kbar) and is accompanied by the development of asymmetric similar folds in the paragenesis with cleavage foliation. The third metamorphism stage (diaphthoresis) in paragneisses means the development of secondary changes. The calculated crystallization temperatures of chlorites correspond to the facies of green shales (T=285-232°C).

The granite pegmatites of Afghanistan are known for deposits of rare metals: Li, Be, Cs, Ta, Nb, Rb, Sn, etc. Ores in the Darai Pech valley of the Kunar province contain crystals of beryl, spodumene, pollucite, and tantalite and are of interest to industry. The article discusses the petrographic features of pegmatite bodies, their internal structure, and the morphological parameters of ore bodies. Particular attention is paid to changes in the mineralogical composition of pegmatite bodies depending on the vertical distance from the parent intrusive rock.

Over 20 pegmatite bodies have been studied. Four types of pegmatite veins are identified with distance from the granite intrusion: 1) essentially plagioclase-microcline, biotite-muscovite pegmatites with rare beryl, schorl, and garnet; 2) albitized microcline and microcline-albite pegmatites with coarse-crystalline beryl, tantalite-columbite, schorl, kunzite, and polychrome tourmaline; 3) albite pegmatites with rare spodumene, finely disseminated beryl, and columbite-tantalite; 4) albite-spodumene pegmatites with columbite-tantalite, cassiterite, clevelandite, lepidolite, kunzite, and polychrome tourmaline. Simultaneously, content of biotite decreases and those of muscovite and clevelandite increase, which positively correlates with contents of rare metal mineralization, piezo-optical raw materials, and precious stones.

Individual pegmatite veins have asymmetrical zoning: the footwall has relatively fine- and medium-grained rocks and the hanging wall – coarse-grained rocks.

In the South Timan, outcrops of the Riphean basement are exposed in the cores of the Dzhezhimparma, Ochparma and Vadyavozh anticlinal structures. The results of U-Pb isotope dating of detrital zircon grains from terrigenous sediments of the middle formation of the Dzhezhim Formation, located in the Vadyavozh quarry, are presented. The rocks were formed no earlier than at the boundary between the Lower and Upper Proterozoic. The age of zircon grains ranges from 3170±43 to 1480±49 Ma. In South Timan, the source of clastic material for the metasandstones of the Dzhezhim Formation is assumed to be crystal complexes of the central parts of the Volga-Ural region. The ages of dated zircons from the lower subformation of the Dzhezhim Formation of the Dzhezhimparma Upland partially coincide with the ages of zircons from the middle subformation of the Dzhezhim Formation, with exception of the Middle-Upper Riphean dating. The grains of detrital zircon contained in the studied metasandstones are much older than the stratigraphic analogues from the northern and middle parts of the Timan Ridge, as well as the Polar and Subpolar Urals. When comparing the data on dating of detrital zircons in the northern and southern sections, a number of differences were established. The majority of zircons from the northern part of Timan are of Middle Riphean age, whereas the number of zircons of Archean and Early Proterozoic age is insignificant. In the South Timan, when studying the age of detrital zircons, the opposite pattern was established: ancient zircons counting 2100 and 2500 million years predominate, and zircons of Middle Riphean age are absent. The formation of Riphean rocks in the South Timan originated from more ancient (Archean-Early Proterozoic) sources, in contrast to the basement rocks in the Middle and North Timan, where the sources were younger (Middle Riphean) complexes.

The accident was registered in the Zuevka District of the Kirov Region in the upper reaches of the Cheptsa River on December 26, 2023. The purpose of this work is to analyze seismic data obtained by regional seismic stations, calculate the main parameters of the seismic event happened on December 26, 2023, and determine the seismotectonic position of the epicentre. The seismic event was recorded by seismic stations of the Komi Republic, Bashkortostan, the Perm Territory, Arkhangelsk, Kirov, Orenburg, Samara, Saratov, and Sverdlovsk Regions. The event was analyzed using wave forms of 24 stations with epicentral distances from 81 to 1352 km, azimuthal environment – 18–359.5°, GAP=80°.

The instrumental processing gave the following parameters of the December 26 earthquake: coordinates 58.4843N, 50.794E, origin time t₀=01:44:36 (UTC), depth h=4 km, energy class according to T.G. Rautian Kp=10.2/4, local magnitude ML=3.6/5, Ms=2.7/5, error ellipse: Az_major=60°, R_minor=4.5 km, R_major=5.5 km. The earthquake is tectonic and belongs to the Kirov-Kazhim aulacogen of the Volga-Ural anteclise. The area is known for serious historical earthquakes; instrumental disturbances are also regularly recorded here. The previous activation of the aulacogen occurred in 2020, also in its central flank. The occurrence of seismic events indicates that it is a seismically active structure.

The paper highlights the results of complex mineralogical, spectroscopic, chromatographic, isotope-geochemical studies of the remains of the Taimyr mammoth, including bones, bone collagen, hairs, skin and soft – muscle and fatty – tissues, obtained for the first time. The authors have drawn conclusions about the animal's biological age, paleoclimatic conditions of existence, diet, as well as about the forms and degree of fossilization of its fossil remains.

The article is devoted to the analysis of the organizational and scientific activities of N. I. Timonin, Doctor of Geology and Mineralogy, a famous scientist in the field of geotectonics and geology of combustible minerals who made a significant contribution to the study of the geological structure of the Pechora Plate. In spite of the fact that the geological research in the Timan-Pechora oil and gas province has a rather long history, there are still many unsolved questions regarding the geological structure of the territory, oil and gas prospects, development of the mineral resource base. The research is going on, and the continuity of knowledge is an extremely important factor for its fairness and the basis for further discoveries.

During the preparation of the article, we have analyzed the published and archive works of N. I. Timonin who devoted 50 years of his life to the geological studies of the Pechora Plate, Timan, the Urals, Pay-Khoy, and the islands of Vaygach and Novaya Zemlya.