pdf № 278, February

DOI: 10.19110/2221-1381-2018-2-3-9

The article presents an overview of the finds of Mesozoic rocks on the territory of the Yugor Peninsula. Previously it was believed that the Mesozoic deposits were not preserved on the peninsula’s territory (with the exception of the Kara astroblem), but nevertheless throughout the history of the geological study of the Ugra peninsula, the researchers encountered blocks and boulders of rocks attributable to the Cretaceous formation time from finds of faunal remains. The article contains information about new finds, summarizes the materials on Cretaceous sediments of predecessors and substantiates the hypothesis of its autochthon origin. The available materials allow us to conclude that the Cretaceous period is fragmentarily preserved on the territory of the Ugra Peninsula. They can be represented both by lithotified varieties and by loose rocks, as a result of which they can be taken as Neogene-Quaternary formations. In the Cretaceous, the coastal and marine conditions of sedimentation prevailed on the territory of the Ugra Peninsula.

Keywords: Ugra peninsula, Pai-Khoi, Mesozoic, Cretaceous, Ammonoidea, Bivalvia.

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DOI: 10.19110/2221-1381-2018-2-10-17

 Evidences of hot accretion of the Earth and the formation of kimberlites from residual melts of the lower peridotite layer of the magmatic ocean are given. They explain the high content of melt components in diamonds, later their formation in the history of the Earth and explain Clifford’s rule. The diamonds were crystallized as a result of the accumulation of carbon in the residual melt, an increase in the degree of supersaturation of the melt by carbon during magmatic fractionation led to a change in layerwise growth by radial and the evolution of the crystallomorphology of diamonds in the direction octoctahedra to dodecahedroids and then to cubes and clusters. This explains the formation of faceted microsculptures. The accumulation of impurities in the melt is the reason for the increase in the content of nitrogen and light carbon isotope in the late diamonds.

Keywords: the origin of diamonds and kimberlites, the Clifford rule.

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DOI: 10.19110/2221-1381-2018-2-18-27

The paper provides new data related to the accessory minerals found in ashes from phreatic eruption of Klyuchevskoy volcano in 2008—2009. We characterized form of extraction, composition and specific features of garnet, corundum, deltalumine, muassonite, sulfide thallium, native metal and carbon phases including micro-diamond, and also likely abiogenic condensed organic compound. A feature of the Koryak diamonds is a very small size and a cubic habit, which may indicate their crystallization from the gas phase under conditions of significant super saturation along the carbon. The detection of various particles and filaments of condensed organic compounds in the form and color in the ash of the Koryak volcano confirms the previous conclusion about systematic inorganic synthesis of highly organized prebiological forms of organic matter in modern volcanoes.

Keywords: Kamchatka, Koryaksky volcano, ashes, accessory minerals, diamond, organic compounds.

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DOI: 10.19110/2221-1381-2018-2-28-37

We present results of our study of main placer-forming minerals of ilmenite placer. Ilmenite placer is similar to other occurrences in weakly-lithified greywacke Triassic sandstones in the eastern part of the Bolshesyninskaya basin of the Pre-Ural foredeep. The placer is characterized by high contents of ilmenite (up to 102 kg/m3) and substantially differs by its structure and formation conditions from known industrial zircon-ilmenite placers. The determination of potential for the titanium content of Triassic rocks of the region required the solution of problem of identifying source of ilmenite. The study of the typomorphic properties of ilmenite and minerals-satellites concluded — epidote-amphibolite schists or amphibolites were the most likely primary source.

Keywords: ilmenite, Middle Triassic, Pre-Ural foredeep.

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DOI: 10.19110/2221-1381-2018-2-38-47

Mantle and crustal peridotites contain principally different petrogenetic information. The former characterize composition and thermodynamic conditions of mantle restitic material emplaced into the crust, the latter reflect multistage metamorphic evolution of crustal magmatic protoliths. Chemical peculiarities of garnet from garnet peridotites of Marun-Keu UHP-complex from Polar Urals (N. Russia) in comparison with garnet from crustal and mantle peridotites of different collision zones were study. The relic areas of plagioclase-bearing protoliths in garnet peridotite bodies of Marun-Keu Complex are obvious evidence of their crustal low pressure origin. The composition of garnet from Marun-Keu UHP-ultramafics is similar to crustal UHP-peridotites of collision zones of N. Kazakhstan, W. Norway, N.-W. China and E. China. Thermobarometric comparison showed that PT-conditions are not the reason of chemical differences of peak garnets from two genetic types of peridotites. Multiple chemical composition of peak metamorphic garnets as a function of petrochemical composition of peridotites can be used as indicator of crustal/mantle genesis of ultramafics in UHP-collision zones.

Keywords: Marun-Keu Complex, Polar Urals, garnet, crustal and mantle peridotites, UHP-metamorphism.

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