PHYSICOCHEMICAL PARAMETERS OF CRYSTALLIZATION OF MELTS IN INTERMEDIATE SUPRASUBDUCTION CHAMBERS (by the example of Tolbachik and Ichinskii Volcanoes, Kamchatka Peninsula)
N.L. Dobretsov1,2, V.A. Simonov3,2, A.V. Kotlyarov3, R.Yu. Kulakov2, N.S. Karmanov3
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: Physicochemical parameters of crystallization, intermediate suprasubduction chambers, melt inclusions, basalt and andesite minerals, Kamchatka volcanoes
Abstract
In study of plagioclases, amphiboles, and melt inclusions, we have determined the physicochemical parameters of crystallization of melts in the intermediate suprasubduction chambers of volcanoes representing different types of subduction magmatism on the Kamchatka Peninsula: the young basaltic systems of Tolbachik Volcano (Klyuchevskaya group) and ancient Ichinskii Volcano (Sredinnyi Range) with alternating basaltic and felsic eruptions. For Tolbachik Volcano, we have found that plagioclase lapilli formed from basaltic melts at 1075-1115 ºC and low (≤1 kbar) pressures at depths of 2-3 km. Andesite minerals crystallized within a wider range of temperatures and pressures (1220-1020 ºC and 3.3-1.6 kbar) in an intermediate chamber at depths of ≤10 km. The melts were generated in basaltic magma chambers (detected well by geophysical methods at depths of 18-20 km) with minimum temperatures of ~1290 ºC. For Ichinskii Volcano, three levels of intermediate chambers are distinguished. Andesites formed at depths of ≤23 km at ≤1225 ºC. Dacitic melts were generated from an intermediate chamber (14 km) at 1135-1045 ºC as a result of differentiation of andesitic magmas. Dacites formed in the uppermost horizons (9-3 km) at 1130-1030 ºC. Despite the similarity between differentiation processes in the intermediate chambers of the Kamchatka volcanoes, each volcano is characterized by specific magmatism. The lavas of basaltic volcanoes (Tolbachik) and those of andesitic volcanoes (Ichinskii) differ in genesis and differentiation.
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