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Date submitted2024-03-11
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Date accepted2024-09-24
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Date published2024-12-06
Comparative analysis of nitrogen and carbon isotopic fractionation during diamond formation based on β-factor determination
- Authors:
- Dmitrii P. Krylov
First quantitative estimates are presented for nitrogen isotopic fractionation during diamond crystallization with respect to nitrogen-bearing fluid components using quantum-mechanical (DFT) calculations on the defect (with the substitutional nitrogen) diamond lattice. Provided equilibrium isotopic fractionation, 15N/14N ratio decreases within the sequence of compounds NH4+ > N2 > (diamond, NH3) > CH3N > CN− > NH2. At temperatures of 1,100 to 1,200 °C fractionation among diamond and fluid N-compounds are estimated at –2.23, –0.77, 0.01, 0.44, 1.31 and 2.85 ‰ and substantially (over 1 ‰) exceed the already available estimates based on the modeling diamond C-N bonds by analogy with HCN or CN – molecules. Depending on the dominant nitrogen and carbon substance in the mineral-forming fluid, diamond formation can be accompanied by different isotope compositional trends, as expressed either by zoned patterns within individual diamond grains or by isotopic δ15N vs δ13C covariations during successive crystallization. Provided the dominance of NH3 component (the reduced conditions, high pressures and the cold geotherm) nitrogen isotope fractionation between diamond and fluid does not exceed 0.1-0.2 ‰ and the isotope shifts at temperature ca. 1100 °C Δ15N << Δ13C. In nitrogen depleted reduced mantle fluids possible existence of compounds with low heavy isotope affinity at temperature of diamond formation (especially NH2) implies high isotope fractionation between diamond and the fluid and hence, evolved Δ15N/Δ13C ratios. Oxidized fluids dominated by CO2 or CO3 coupled with N2 component are characterized by close to zero Δ15N/Δ13C ratios as inferred by prevailing carbon isotope fractionation with respect to nitrogen isotopes, the latter change considerably with nitrogen distribution coefficient among diamond and the growth media.
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Date submitted2023-02-07
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Date accepted2023-06-20
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Date published2024-02-29
Origin of carbonate-silicate rocks of the Porya Guba (the Lapland-Kolvitsa Granulite Belt) revealed by stable isotope analysis (δ18O, δ13C)
- Authors:
- Dmitrii P. Krylov
- Ekaterina V. Klimova
Carbonate-silicate rocks of unclear origin have been observed in granulites of the Porya Guba of the Lapland-Kolvitsa Belt within the Fennoscandinavian Shield. The present work aims to reconstruct possible protoliths and conditions of metamorphic transformation of these rocks based on oxygen and carbon isotopic ratios combined with phase equilibria modeling. Isotope analysis and lithochemical reconstructions suggest that carbonate-silicate rocks of the Porya Guba represent metamorphosed sediments (possibly marls) with the isotopic composition corresponding to the Precambrian diagenetically transformed carbonates (δ18O ≈ 17.9 ‰, SMOW and δ13C ≈ –3.4 ‰, PDB). The chemical composition varies depending on the balance among the carbonate, clay, and clastic components. Significant changes of the isotopic composition during metamorphism are caused by decomposition reactions of primary carbonates (dolomite, siderite, and ankerite) producing CO2 followed by degassing. These reactions are accompanied by δ18O and δ13C decrease of calcite in isotopic equilibrium with CO2 down to 15 ‰ (SMOW) and –6 ‰ (PDB), respectively. The isotopic composition is buffered by local reactions within individual rock varieties, thus excluding any pronounced influence of magmatic and/or metasomatic processes.
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Date submitted2022-03-20
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Date accepted2022-05-25
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Date published2022-07-26
Ophiolite association of Cape Fiolent (western part of the Mountainous Crimea) – the upper age constraint according to the U-Pb isotope dating of plagiorhyolites (Monakh Cliff)
The article presents the results of U-Pb isotope dating (SHRIMP-II, VSEGEI, Saint Petersburg) of zircon crystals extracted from plagiorhyolites of the Monakh Cliff in the area of Cape Fiolent in the western part of the Mountainous Crimea (southern suburb of Sevastopol). a concordant age estimate of 168.3±1.3 Ma was obtained from 20 zircon crystals. It exactly corresponds to the Bajocian/Bathonian boundary of the Middle Jurassic according to the International Chronostratigraphic Chart (February 2022 version). The available results of isotope dating of igneous rocks from the Mountainous Crimea, as well as their geochemical typification are synthesised. The plagiorhyolites of the Monakh Cliff in the area of Cape Fiolent are spatially, and most likely paragenetically, associated with the wallrock (Cape Vinogradny) and ore (Heraclea Plateau on the cognominal peninsula) massive sulphide formations, as well as pillow basalts, gabbroids, and serpentinized hyperbasites, combined into the ophiolite association of Cape Fiolent. The obtained dating is the upper age limit for the entire ophiolite association of Cape Fiolent.
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Date submitted2009-08-16
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Date accepted2009-10-15
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Date published2010-02-01
Analysis and synthesis of commercial oil using radioisotope measuring the density
- Authors:
- I. N. Voityuk
This article deals with a system of commercial accounting of oil transported using radioisotope measuring the density, i.e. measurement-wise number of borehole fluid. In this paper we developed a connection diagram for measuring the density of radioisotope in the main pipeline and verification tools for the measurement system.