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Date submitted2023-04-04
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Date accepted2023-09-20
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Date published2024-08-26
Association of quartz, Cr-pyrope and Cr-diopside in mantle xenolith in V.Grib kimberlite pipe (northern East European Platform): genetic models
The first results of mineralogical and geochemical studies of a unique xenolith of lithospheric mantle are presented illustrating the earlier non-described mineral association of quartz, Cr-pyrope and Cr-diopside. Structural and textural features of the sample suggest a joint formation of these minerals. The calculated P-T-parameters of the formation of Cr-diopside indicate the capture of xenolith from the depth interval ~ 95-105 km (31-35 kbar) corresponding to the stability field of coesite. This suggests that quartz in the studied xenolith can represent paramorphs after coesite. It was shown that quartz in this rock is not a product of postmagmatic processes. The transformation stage of the source lherzolite into garnet- and clinopyroxene-enriched rock/garnet pyroxenite as a result of exposure to a high-temperature silicate melt was reconstructed. Subsequent stages of the influence of metasomatic agents were identified by the presence of a negative Eu-anomaly in some garnet grains, which could result from the impact of subduction-related fluid and the enrichment of rock-forming minerals with light rare earth elements, Sr, Th, U, Nb and Ta as a consequence of fluid saturated with these incompatible elements. Several models for the formation of SiO2 phase (quartz/coesite) in association with high-chromium mantle minerals are considered including carbonatization of mantle peridotites/eclogites and melting of carbonate-containing eclogites at the stage of subduction and the impact of SiO2-enriched melt/fluid of subduction genesis with peridotites of the lithospheric mantle.
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Date submitted2022-11-29
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Date accepted2023-03-02
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Date published2023-10-27
New data on the composition of growth medium of fibrous diamonds from the placers of the Western Urals
This article presents the results of studying microinclusions of fluids/melts in diamonds from the placers of the Krasnovishersky District (western slope of the Middle/Northern Urals), which make it possible to establish the evolution of diamond-forming media in the subcontinental lithospheric mantle of the eastern margin of the East European craton. Impurity composition of the studied crystals reveals three different types of diamonds, the formation of which was associated with separated metasomatic events. Microinclusions in B-type diamonds containing A and B nitrogen defects reflect an older metasomatic stage characterized by the leading role of silicic and low-Mg carbonatitic fluids/melts. The second stage is associated with the growth of A-type diamonds containing nitrogen exclusively in the form of A-centers. At this stage, the formation of diamonds was related with low-Mg carbonatitic media, more enriched in MgO, CaO, CO2, and Na2O compared to B-type diamonds. The third stage probably preceded the eruption of the transporting mantle melt and led to the formation of C-type diamond containing A and C nitrogen defect centers and microinclusions of silicic to low-Mg carbonatitic composition. The recorded trend in the evolution of diamond-forming fluids/melts is directed towards more carbonatitic compositions. Fluids/melts are probably sourced from eclogitic and pyroxenitic mantle substrates.
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Date submitted2022-02-22
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Date accepted2022-09-15
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Date published2022-11-10
The problem of the genesis of the Mesoarchean aluminosilicate rocks from the Karelian craton and their possible use as a quartz-feldspar raw material
The article presents original data obtained in the study of the chemical and mineral compositions of the Late Archean aluminosilicate rocks (formerly called silicites) from the Koikari and Elmus structures of the Vedlozero-Segozero greenstone belt of the Karelian craton (Central Karelia). A comprehensive study of these formations revealed their complex genesis as a result of the late imposition of hydrothermal and metamorphic alteration on sedimentary and volcanic-sedimentary rocks of feldspar-quartz composition. Due to the superimposed metasomatic (temperature?) impact on feldspar-quartz siltstones, Fe was removed from microinclusions in quartz and feldspar and its oxides were concentrated along the grain boundaries. Minerals such as monazite, parisite, allanite are also located either along the grain boundaries of quartz and feldspars, or together with calcite they fill microfractures, which makes it possible to get rid of them when preparing quartz-feldspar concentrates using various beneficiation technologies. According to most indicators limited by GOSTs, individual samples in their natural form meet the requirements for quartz-feldspar raw materials for use as part of batch in the production of diverse types of glass. Additional beneficiation of the feedstock (grinding, screening into narrow classes and further magnetic separation) leads to a decrease in Fe 2 O 3 content to normalized values. The resulting quartz-feldspar concentrates with various particle sizes can be used in the production of building material and fine ceramics (sanitary and ceramic products, facing and finishing tiles, artistic, household porcelain and faience). The homogeneity of the mineral and chemical composition, the possibility of compact extraction and beneficiation (including in mobile small-sized installations) increase the prospects and competitiveness of this non-traditional feldspar raw material from Central Karelia.
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Date submitted2008-10-22
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Date accepted2008-12-14
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Date published2009-12-11
Peculiarities of structure and comparative analysis of oil-and-gas basins in the Pacific segment of lithosphere
- Authors:
- V. B. Archegov
Comparative analysis was carried out for oil-and-gas-bearing basins of young and oldland platforms of the Pacific segment. Previously the same kind of analysis had been realized for the Atlantic segment of lithosphere. Obtained results confirm the unique geological structure and oil-and-gas capacity of Siberian platform, by these features it differs from all other cratons in the whole world.