VOLATILE СONTENTS DURING THE FORMATION OF OLIVINITE AND OLIVINE-MONTICELLITE ROCKS OF THE KRESTOVSKAYA ALKALINE–ULTRABASIC CARBONATITE INTRUSION, POLAR SIBERIA: PYROLYSIS-FREE GAS CHROMATOGRAPHY-MASS SPECTROMETRY DATA

The parental larnite-normative alkaline ultramafic melt consistently forming olivinite and olivine-monticellite rocks of the Krestovskaya alkaline-ultrabasic carbonatite intrusion is enriched with hydrocarbons (HC) and their derivatives, nitrogenated, chlorinated, fluorinated, sulfonated compounds, as well as H₂O and CO₂ according to pyrolysis-free gas chromatography-mass spectrometry data (GC-MS). The aliphatic, cyclic, oxygenated compounds, and very few heterocyclic compounds are determined among the hydrocarbons. During the crystallization of olivine in olivinites, fluids are enriched in hydrocarbons (59.30 rel. %), excluding nitrogenated, chlorinated, and sulfonated derivatives and including predominant amount of oxygenated compounds (52.17 rel. %) and subordinate amount of aliphatic and cyclic compounds (6.70 rel. %). During the crystallization of perovskite in olivine-monticellite rocks, the amount of oxygenated hydrocarbons slightly decreases (34.77 rel. %) and aliphatic and cyclic compounds increases up to 10.55 rel. %. The crystallization of monticellite is accompanied by the predominance of aliphatic and cyclic hydrocarbons (59.67 rel.%) and subordinate amounts of oxygenated hydrocarbons (29.35 rel. %). The fact that the calculated H/(O + H) ratio is 0.78 and 0.77 for fluids in olivine and perovskite, respectively indicates the reducing conditions of crystallization of these minerals. On the stage of olivine crystallization of olivinite, the fluids also contain 4.1 rel. % of nitrogenated, 4.58 rel. % of sulfonated, 0.19 rel. % chlorinated, 0.12 rel. % fluorinated hydrocarbons, 0.49 rel. % CO₂, and 31.17 rel. % H₂O. The crystallization of perovskite in olivine-monticellite rocks is accompanied by further accumulation of nitrogenated compounds up to 8.95 rel. %, sulfonated (9.53 rel. %) and chlorinated (11.33 rel. %) hydrocarbons, and 16.48 rel. % CO₂. In this stage the content of H₂O in the fluids decreases to 7.66 rel. % due to its binding to cations and Al-Si-radicals of the melt into hydroxyl-bearing compounds. At the final stage of crystallization of perovskite and initial monticellite, when fluids are saturated by critical amounts of chlorinated, nitrogenated and sulfonated compounds and CO₂, they become to dissolve in the melt and react with it: most of the considered fluids, together with Ca and alkalis of the melt, form carbonate-salt compounds and the melt became silicate-salt composition. According to GC-MS analysis data, residual fluid phase of monticellite-hosted inclusions are characterized by only 2.29 rel. % nitrogenated and 1.11 rel. % sulfonated, 0.32 rel. % chlorinated, and 0.35 rel. % fluorinated hydrocarbons, 0.04 rel. % CO₂ and 6.15 rel. % H₂O with an increase in hydrocarbons up to 89.63 rel. %. During the crystallization of monticellite, silicate-salt immiscibility occurred, followed by spatial separation of the silicate and salt fractions.