Volatile Contents 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 (kamafugite) melt sequentially 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, volatiles 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 that of 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 calculated H/(O + H) ratio of 0.78 and 0.77 for volatiles in olivine and perovskite, respectively, indicates the reducing conditions of crystallization of these minerals. On the stage of olivine crystallization in olivinite, the volatiles also contain 4.1 rel % of nitrogenated, 4.58 rel % of sulfonated, 0.19 rel % of chlorinated, 0.12 rel % of fluorinated hydrocarbons, 0.49 rel % CO₂, and 31.17 rel % H₂O. The crystallization of perovskite in the olivine-monticellite rocks is accompanied by the 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. At this stage, the content of H₂O in the volatiles 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 perovskite crystallization and the initial stage of monticellite crystallization, when volatiles were saturated in the 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 volatiles, together with Ca and alkalis of the melt, form carbonate–salt compounds and the melt became silicate–salt in composition. According to GC–MS data, a residual gaseous phase of monticellite-hosted inclusions is 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 at an increase of hydrocarbons up to 89.63 rel %. The crystallization of monticellite was accompanied by the silicate–salt immiscibility that was followed by the spatial separation of the silicate and salt fractions.