O.Yu. Tsymbal
https://orcid.org/0000-0002-8800-9899
S.G. Kryvdik
https://orcid.org/0000-0002-8356-1115
M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of the NAS of Ukraine 34, Acad. Palladin Ave., Kyiv, Ukraine, 03142
https://doi.org/10.15407/gof.2024.45.013
Microprobe analyses of nepheline from alkaline-ultrabasic rocks (melteigites) in North-Western region of the Ukrainian are given. The nepheline is more often substituted by cancrinite, natrolite and spreustein. Studied nepheline turned out most natrium comparatively to nephelines from other alkaline massifs of the Ukrainian shield. Natrium composition of nepheline (Ne 77—89, Ks 5—13, Q 2—12 wt. %) is in concordance with natrium type of fenites in exocontacts halo of alkaline-ultrabasic intrusions in this region. In other regions similar hypabissal intrusions are characterized by predominantly potassic fenites. Natrium nepheline together with other petrological (high magnesian primitive rock composition) and geochemical (very low concentration of rare incoherent elements Nb, REE as well as P2O5) peculiarities make studied alkaline-ultrabasic rocks non-typical, unique.
Key words: Natrium nepheline, alkaline-ultrabasic rocks
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