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Denis S. Mikhailenko
Denis S. Mikhailenko
Senior Researcher, Ph.D.
V.S.Sobolev Institute of Geology and Mineralogy Siberian Branch RAS
Senior Researcher, Ph.D.
V.S.Sobolev Institute of Geology and Mineralogy Siberian Branch RAS
Novosibirsk
Russia

Articles

Geology
  • Date submitted
    2023-04-04
  • Date accepted
    2023-09-20
  • Online publication date
    2023-12-19
  • Date published
    2024-08-26

Association of quartz, Cr-pyrope and Cr-diopside in mantle xenolith in V.Grib kimberlite pipe (northern East European Platform): genetic models

Article preview

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.

How to cite: Agasheva E.V., Mikhailenko D.S., Korsakov A.V. Association of quartz, Cr-pyrope and Cr-diopside in mantle xenolith in V.Grib kimberlite pipe (northern East European Platform): genetic models // Journal of Mining Institute. 2024. Vol. 268. p. 503-519. EDN HLLHDR
Geology
  • Date submitted
    2022-12-01
  • Date accepted
    2023-01-19
  • Online publication date
    2023-05-18
  • Date published
    2023-12-25

Inclusions of diamond crystals in the tourmaline of the schorl-uvite series: problems of genesis

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The mineralogical and geochemical features of diamond-bearing tourmaline crystals (schorl-uvite series) from garnet-clinopyroxene rocks of the Kumdy-Kol deposit (Northern Kazakhstan) have been studied in detail. The formation of the main rock-forming minerals (garnet + K-bearing clinopyroxene) occurred in the diamond stability field at 4-6 GPa and 950-1000 °C. Crystallization of K-bearing clinopyroxene at these parameters is possible in the presence of an ultra-potassic fluid or melt formed because of crustal material melting in subduction zones. Tourmaline crystals (up to 1 cm) containing diamond inclusions perform veins crosscutting high-pressure associations. The composition of individual zones varies from schorl to uvite within both a single grain and the sample as a whole. The potassium content in this tourmaline does not exceed 0.1 wt.% K2O, and the isotopic composition of boron δ11B varies from –10 to –15.5 ‰, which significantly differs from the previously established isotopic composition of boron in maruyamaite crystals (δ11B 7.7 ‰ in the core and –1.2 ‰ in the rim) of the same deposit. Analysis of the obtained data on δ11B in the tourmalines from the diamond-grade metamorphic rocks within the Kumdy-Kol deposit suggests the existence of two boron sources that resulted in crystallization of K-bearing tourmaline crystals (maruyamaite-dravite series) and potassium-free tourmalines of the schorl-uvite series.

How to cite: Korsakov A.V., Mikhailenko D.S., Zhang L., Xu Y.-G. Inclusions of diamond crystals in the tourmaline of the schorl-uvite series: problems of genesis // Journal of Mining Institute. 2023. Vol. 264. p. 833-841. EDN UMQOXK