No 3 (2024): Науки о Земле
Articles
The Kraka lherzolite massifs (Southern Urals): geochemistry, geochronology, genesis, geodynamics
Abstract
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.



Petrology of granites of the Kozhim massif (Subpolar Urals)
Abstract
The paper presents the study results on granites of the Kozhim massif (the Subpolar Urals). The joint Kozhim massif earlier included the Kuzpuayu granite body. It lies to the north of the Kozhim massif. For this reason, many previously obtained conclusions were summarizing. The detailed study on rocks that included analyses of cuts, accessory and ore mineralization, petrogenic and rare elements was conducted in the Geoscience subdivision at the Institute of Geology, Komi Science Centre of the Ural Branch of the Russian Academy of Sciences. This study helped to clarify and supplement the information about the granitogenesis of the considered massif. According to the obtained data, the granites under study are high-potassium high-alumina leucogranites of normal and moderate alkalinity with high content of orthoclase and the presence of plagioclase of two generations. The rocks were formed under intraplate and post-collision geodynamic conditions from crustal parent melts enriched with lanthanum and cerium. These melts are characterized by the dependence of potassium and titanium concentrations on changes in silica content.



Paragneisses of the Nyartinskiy metamorphic complex and the Mankhobeinskaya suite (Subpolar Urals): metamorphism, mineral and structural properties
Abstract
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).



Diorites of the Dioritoviy massif (Polar Urals): geochronological and isotope-geochemical data
Abstract
For the first time, the Lu-Hf isotope system of zircons from rocks of the Dioritoviy massif has been characterized and the results of U-Pb (SIMS) dating and the micro-elemental composition of zircons from this massif have been examined in detail. By the petro-geochemical and isotope-geochemical data, diorites of the massif have been found to be formed in the Early and Middle Devonian (Emsian-Eifelian) time in the island-arc geodynamic conditions of a juvenile mantle (almost coeval with diorites) protolith, as indicated by ɛHf(t) positive values and TDM(2) model age.



Internal structure and patterns of distribution of mineral types of rare metal pegmatites in the Darai Pech valley (Kunar province, Afghanistan)
Abstract
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.



Features of the composition and formation of diamond placers in the marginal parts of ancient cratons (on the example of the North-East of the Siberian platform)
Abstract
Summarizing a significant amount of factual material on the complex study of diamond, we have prepared its characterization in the modern strata of the marginal parts of the main diamondiferous regions of the Siberian Platform. The established characteristics on the morphology, coloring, solid inclusions, internal structure, photoluminescence, as well as the impurity composition of diamond, testifies to a multiple number of the primary sources of diamonds from placers and the presence of new, yet undiscovered kimberlite bodies, including those with high content of the useful component, within the region. The studied diamonds from modern placers in the diamondiferous areas of the Leo-Anabar subprovince are relatively homogenous and, in general, are close to the crystals from the older secondary reservoirs surrounding the placers. On the whole, the described placers and diamond occurrences are characterized by a low diamond content of kimberlite type. The presence of relatively “fresh” diamonds of the Lower Lena type in modern placers of this region (without mechanical wear and weakly ferruginized stones) is also a distinctive feature of the modern placers of the region. The typomorphic features of diamonds obtained during the research can be successfully used for zoning of the area concerned in the course of geological prospecting works.



U/Pb age and sources of detrital zircon from Upper Riphaean sandstones of the Nemskaya Upland (South Timan)
Abstract
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.



Integrated interpretation of geophysical data in the area of local gravity anomalies in the North of the Volga-Ural anteclise
Abstract
The complex work uses only original materials of both the measurement results using the Golden Software SURFER program and the results of reconnaissance geological and geophysical field surveys carried out in 2017-2023. The study covered the area of junction of the Kirov-Kazhim trough, the Komi-Permian arch of the Volga-Ural anteclise with the Vychegda trough of the Mezen syneclise, complicated by the rocks of the Lokchim “trap” field in the area of high-intensity local gravitational anomalies we discovered. The clusters of local magnetic anomalies have been identified in the Frolovsk and Chetdin areas and a single one – in Lokchim. Frolovsk is enriched with unrounded chrome spinels, the Cr2O3 content in some of them exceeds 64 % [1]. On the periphery of the intense Chetdin gravitational anomaly, we have discovered the same-name radon anomalous zone with high values of volumetric radon activity [2, 3].
The study results on the miragenic characteristics of the Chetdin location seem to be related to the formation features of the Kirov-Kazhim trough of the Volga-Ural anteclise, those of the Frolovsk location – to the pre-Mesozoic magmatism of the “basic” composition (?) in the area of edge dislocations of the northern end of the Volga-Ural anteclise, and Lokchim – to the defluidization products of decompressed magnetic rocks on the steep western side of the Komi-Permian arch.



Earthquake on December 26, 2023 in the Kirov-Kazhim aulacogen
Abstract
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: Azmajor=60°, Rminor=4.5 km, Rmajor=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.



Relationship between the dynamics of landslide process in the Vorkuta River valley and the main climatic parameters
Abstract
Erosion due to frozen and hygrogenic creep and flooding of the slope with surface waters are the reasons for the landslide revival in residential areas of Vorkuta. We have evaluated the interlink between landslide dynamics, seasonal frost depth and main climatic parameters affecting the above indexes as snow accumulation, mean air temperature of cold year period, number of cold days and amount of liquid precipitation for 2010–2020. Frost depths for technogenic grounds and semi-rocks have been calculated by two methods based: 1 – on the thermal properties of soils and rocks and some climatic parameters, 2 – on the heat conductance of a three-layer medium (snow cover, frozen and thawed soils) and its heat balance. The mean difference between the calculated and some observed frost depths in technogenic grounds is 30 %. The correlation coefficient Kcor was 0.86 and 0.62. According to the Grey correlation analysis, the mean air tem-perature for the cold year period is an important parameter affecting the reference sequence, i.e. landslide dynamics. Cold period length and air temperature best affected the frost depth. Liquid precipitation amount is found to be another significant parameter for both reference sequences.



Pre-Holocene Taymyr mammoth Petya: mineralogical-isotope-geochemical properties of bones, soft tissues, skin, hairs and paleoecologic reconstructions
Abstract
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.



Characteristics of gallstones with crystal structure
Abstract
The article presents the study results of the composition and structure of gallstones with crystal structure. Cholesterol has been confirmed to be the main constituent of crystal gallstones. The studied samples have been identified for inclusions of minerals represented by the following classes as carbonates, oxides, chlorides, sulfates, silicates, and phosphates. The work first mentions the fact that high-carbon cholesterol formations, formed in the human body, by the morphological characteristics of crystals and physicochemical characteristics (behavior when heated, elemental composition) can be classified as analogues of natural crystal resins. The proposed formation mechanisms of gallstones with different structural organizations (spherulite, dendritic, oolitic, columnar aggregates) are discussed.



To the memory of N. I. Timonin who devoted his life to geology
Abstract
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.



To the memory of the geographer-palynologist Evgenia Sergeevna Malyasova (to her 100th birthday)
Abstract
The article is dedicated to the 100th anniversary of the highly qualified palynologist, teacher of many geographers graduated from the Leningrad State University (Department of Geography) Evgenia Sergeevna Malyasova (1923–2020). E. S. Malyasova was a student of I. M. Pokrovskaya, the founder of the Palynological Laboratory at the Department of Geography at the Leningrad State University. She headed the Palynological Laboratory for more than 20 years, gave lectures at the Department of Geomorphology at the Leningrad State University, conducted active scientific research works on the palynology of the Arctic territories and sediments of the White and Barents Seas. The paper contains details of her life and scientific activities.


