pdf № 287, November

DOI: 10.19110/2221-1381-2018-11-3-11

For the first time, among Centeral Alkaline Band (CAB) mylonitic rocks of the Ilmeny-Vishnevogorsky polymetamorphic complex (IVPC) we foundа lenticular body of quarz-biotite- feldspar composition (2 ґ  3 m) with complicated network of thin intersecting recrystallizing veins of metapseudotachylytes. Microscopic research of textural and structural features revealed the presence of two types of metapseudotachylyte veins: early mylonitized metapseudotachylytes and late metapseudotachylytes. In the metapseudotachylyte body discovered Th-U-Y-REE-mineralisation are represented by rare minerals of solid-solution series thorogummite-coffinite and fergusonite-(Y) (REMMA-202 LZ Link systems with Si-Li detector). The composition of the metapseudotachylyte corresponds to normal alkaline granite and has high concentrations of LREE and Th, U, Y (AAS and ICP-MS). The presence of heterochronous metapseudotachylytes indicates a multistage transformation of CAB host rocks, and records the process of partial frictional melting of the rock under stress, in the final stages of formation of the complex.

Keywords: metapseudotachylyte, Ilmeny-Vishnevogorsky polymetamorphic complex.

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DOI: 10.19110/2221-1381-2018-11-12-21

 Despite the relatively weak seismicity of the Komi Republic, its southern part, including Syktyvkar, is referred to a six-point seismic zone on a map of general seismic zoning (GSZ-97 C). It is historically known that in 1939 a seven-point earthquake occurred in the junction zone of the Sysolsky arch and the Kirov-Kazhim aulakogen, which was called the Sysolsky earthquake. This gives us the right to assert that in the future a similar seismic event can be repeated. The greatest number of earthquakes occurred in the Kirov-Kazhim seismogenic zone, which is confirmed by instrumental records of seismograms. An important point is that within the city of Syktyvkar there is a large industrial wood chemical plant, which, according to the status of environmental hazard, belongs to the most critical objects (EIO). Therefore, ensuring the safety of the operation of this enterprise requires detailed seismic zoning (DSZ) and microseismic zoning (SMZ), which can determine the parameters of the ultimate seismic effect on the underlying geological section. In accordance with this, we adhered to the following algorithm for solving the problems posed:

— a two-level assessment of the seismic effects of the maximum estimated earthquake (MEE), which may exceed the estimated seismic hazard of 0.5 % for 50 years and a projected earthquake (DE), where the probability of exceeding the estimated seismic hazard can reach 1 % for 50 years (scale 1 : 2 500 000 — 1 : 1 000 000);

— the set of probabilistic expected seismic impacts on the most important national economic objects was determined
(scale 1 : 500 000 — 1 : 200 000);

— Quantitative assessment of the effect of engineering-geological conditions on the initial seismicity was carried out
(scale 1 : 25 000 — 1:  5 000).

Thus, the main goal of this work is to obtain initial parameters corresponding to strong soil motions for the most unfavorable conditions, when rocky soils are covered by thick Quaternary deposits of the second and third (fourth) soil categories.

Keywords: earthquake, seismodynamic impact, soil category, peak acceleration, dilatancy, elastic state, reaction spectra, accelerogram, zoning.

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DOI: 10.19110/2221-1381-2018-11-22-30

For the first time, a comparative analysis of zircons from metasedimentary, including carbon-containing Upper Proterozoic deposits of the Nyarovei series and the Nemuryugan suite of the Polar Urals was carried out. The study of the typical features of zircons showed differences in the internal structure and chemical composition of the mineral. For meta-sedimentary non-carbonaceous rocks, a flat surface and a homogeneous structure of zircon grains are characteristic. In zircons from carbon-containing deposits, the internal structure is inhomogeneous, there are secondary changes. In the Carboniferous deposits of the Nyarovei series and the Nemuryugan suite, uranium is found in zircon. Zircon originally could be enriched with uranium, or the formation of uranium in initially deformed zircons could be associated with hypergenic processes. In carbon-containing deposits of the Miniseyshor suite in zircons, in addition to uranium, yttrium, thorium and scandium are present.

Keywords: carbon-containing deposits, zircon, the Polar Urals.

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DOI: 10.19110/2221-1381-2018-11-31-37

The new results of studying of the geological structure of the Upper Silurian deposits on the Western slope of the Subpolar Urals are presented. Data analyses and synthesis allow us to establish bio- and event-stratigraphical boundary of the Ludlow-Pridoli and discover disconformity at the terminal Ludlow. These results suggest revision of the correlation of the Ludlow-Pridoli boundary beds of the Subpolar Urals and Estonia.

Keywords: brachiopods, conodonts, Ludlow, Pridoli, δ¹³C_carb.

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DOI: 10.19110/2221-1381-2018-11-38-42

In the structure of the Bol'shaya Kos'yu reef, four intervals corresponding to the phases/ stages of growth are established. The highest biodiversity of the reef ecosystem is typical for interval III, while for the final stage IV — it is the lowest. The frame-building organisms are dominated by stromatoporoids, tabulates and sphinctozoan. For the first time, a wide distribution and taxonomic diversity of sphinctozoan in the Upper Ordovician reefs of the Urals is recognized. They were mostly cryptobionts, lived in environments conducive to other Metazoa, and had, thus, their own ecological niche. However, with the deterioration of living conditions, they quickly adapted to changing environmental conditions and became one of the dominant groups among frame-building organisms.

Keywords: biodiversity, reef, Upper Ordovician, Ilych River, Northern Urals.

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DOI: 10.19110/2221-1381-2018-11-43-47

Based on the analysis of the vast literature on phosphorites, it is determined that a permanent association «phosphorite — glauconite» is a real paragenesis. The reason for this paragenesis is the common facial and diagenetic conditions of Ca-phosphate and glauconite formation and the decisive role of iron in their formation. Frequent change of topographical, dynamical and hydrochemical facies sedimentation in the form of «Baturin's cycles», the support of iron hydroxides (as collector of phosphorus) from the weathering crusts to chelf basin are the cause for diagenetic glauconite and Ca-phosphat formation.

Keywords: phosphorites, glaukonite, geochemistry of phosphorus, geochemistry of iron.

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DOI: 10.19110/2221-1381-2018-11-48-53

The object of the study is modern evaporitic sediments of the Taloe Lake tract. It is located on the territory of the South Minusinsk depression and represents an intercostal cavity with two temporary reservoirs — the Western and the Eastern. The urgency of the work is due to the fact that Taloe Lake belongs to a group of steppe reservoirs, which in turn are characterized by a specific set of mineral species that depend on the composition of the water supplying the reservoir. The investigations made it possible to diagnose the total mineral composition of bottom sediments, as a result of which two mineral associations were identified: evaporite (combines the mineral phases that can be obtained by evaporating brines, groundwater and surface waters) and terrigenous (includes mineral species insoluble in water). Also, a sequence of precipitation of water-soluble minerals from brines was established, through the study of the relationships of mineral phases. At the same time, the mineral composition of the bottom sediments depends directly on the hydrogeochemical type of water.

Keywords: evaporites, mineral association, mineral zonality, sequence of mineral formation.

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