VOLATILES IN SUPRASUBDUCTION BASALTIC MELTS FROM TOLBACHIK VOLCANO (Kamchatka)
N.L. Dobretsov1,2, V.A. Simonov3,2, A.V. Kotlyarov3, S.I. Stupakov3
1A.A. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
3V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Летучие компоненты, надсубдукционные базальтовые расплавы, высокотемпературная газовая хроматография, влк. Толбачик, Камчатка, Volatiles, suprasubduction basaltic melt, high-temperature gas chromatography, Tolbachik Volcano, Kamchatka
Abstract
Vitreous basalts and plagioclase lapilli from Tolbachik Volcano studied by high-temperature gas chromatography reveal features of a fluid regime uncommon to suprasubduction melts. Prominent depletion in volatiles confirms the anomalous behavior of the Tolbachik fluid systems. Vitreous basalts contain minor amounts of water (0.16-0.27 wt.%) and carbon dioxide (95-440 ppm). New data on volatiles in the Tolbachik plagioclase lapilli show very low contents of CO2 and total gas (exclusive of H2O) and enrichment in reduced fluids (CO and CH4) relative to the basalts. In general, analysis of basalts and plagioclase lapilli from different eruptions trace a progressive increase in reduced fluids (CO and CH4) and decrease in CO2 and total gas from past to present events. The concentrations of CO2 decrease, while those of CO and CH4 in basalts and plagioclase lapilli increase systematically with an increase in FeO/MgO ratios and K2O contents in the lavas and in anorthite component in plagioclase.
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