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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 submitted2022-12-03
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Date accepted2023-02-03
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Date published2023-08-28
Garnetites from Marun-Keu eclogite complex (Polar Urals): geochemistry and the problem of genesis
- Authors:
- Laysan I. Salimgaraeva
- Alexei V. Berezin
A comprehensive mineralogical and geochemical characterization (XRF, ICP-MS, SEM-EDS, SIMS methods) of garnetites and their protoliths from the Marun-Keu complex (Polar Urals), one of the key objects in understanding the evolution of the Uralian Orogen, is presented. Garnetites and their protoliths from the Marun-Keu complex, Polar Urals, a key locality for understanding the evolution of the Uralian Orogen, are described mineralogically and geochemically using XRF, ICP-MS, SEM-EDS and SIMS methods. Ultramafic (in most cases) and mafic rocks are understood as protoliths for garnetites. A general trend for garnetites is an increase in total REE concentration relative to that of their protoliths. All the analyzed garnetites display a considerable decrease in Cr, Ni and Co. V concentration in the garnetites is also lower than that of the protoliths, though not so markedly. Garnets from garnetites evolving after peridotites generally exhibit elevated (relative to garnets from garnetites evolving after mafic rocks, such as porphyrites) Prp and lowered Alm content, which seems to be due to high Mg concentration in the protolith. In garnetites after peridotites a garnet exhibiting an uncommon non-differentiated REE spectrum with a considerable positive Eu-anomaly was found, which could be due to the inheritance of a REE spectrum by garnet from a precursor mineral, in this case plagioclase. Slyudyanaya Gorka garnetites were probably formed from mafic and ultramafic rocks in oceanic crust, which migrated to higher levels of the section under the influence of the crustal fluid flowing along fracturing zones.
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Date submitted2009-08-11
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Date accepted2009-10-07
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Date published2010-02-01
Mineralogical and geochemical features of metamorphic roks of Pestpaksha (Kola peninsula)
- Authors:
- A. V. Kurguzova
The rock composition was studied, the garnet composition was researched with a X-ray phase analysis, and equilibrium pressures of the garnet crystallization were calculated with the geobarometer GASP, thermal properties of graphite were characterized and polymorphic modification was identified by X-rays diffraction.
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Date submitted2008-10-17
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Date accepted2008-12-07
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Date published2009-12-11
Morphometry of aggregates and modeling of phase transition kinetics under metamorphism
- Authors:
- Yu. L. Gulbin
The paper discusses some general relations between the structure of metamorphic rocks and mechanisms of phase reactions. Among these relations is the influence of nucleation and growth of kinetics on the crystal size distribution. A brief overview is made of theoretical models which have been proposed to explain granulometric properties of rocks, and kinetic laws and factors on the metamorphic crystallization are considered by the example of metapelitic garnets, including the phenomenon of avalanche nucleation at finite overheating as well as the growth of porphyroblasts under diffusion-limited conditions. As a result, a new approach to modeling of native granulometric curves is presented.