Physicochemical Parameters of Magmatism of the Uksichan and Ichinsky Volcanoes (Sredinnyi Ridge, Kamchatka): Data on Melt Inclusions

—Thermobarogeochemical study of melt inclusions and investigation of clinopyroxenes and amphiboles from effusive rocks of the Uksichan and Ichinsky Volcanoes gave an insight into the parameters of deep-seated melts and the evolution of magmatic systems during the formation of minerals in intermediate chambers. Study of melt inclusions from the Uksichan volcanic rocks made it possible to estimate the pressure during the liquidus crystallization of clinopyroxenes and plagioclases from basaltic magmas and to establish four depth intervals of the formation of these minerals: ~60, 45–30, 27–18, and from 12 km to the subsurface. Comparison of the results of calculation based on melt inclusion data and of the clinopyroxene and amphibole data helped to establish the evolution paths of the P–T parameters of ascending melts of the Uksichan Volcano. The most high-temperature magmas, generated at a depth of ~60 km, are characterized by a successive temperature decrease during their ascent (1320–1240–1200 °С). Based on the representative data on the compositions of amphiboles from the Uksichan and Ichinsky Volcanoes, we have elucidated the general regularities of the evolution of intermediate and acid magmatic systems, with three depths of crystallization in intermediate chambers. Amphiboles of the Ichinsky Volcano andesites and the Uksichan Volcano latites crystallized at depths of 22.0–18.5 and 18–16 km and at temperatures of 980–930 and 1010–985 °С, respectively. As melt ascended to a depth of 15.5–11.0 km and a temperature decreased from 945 to 880 °С, amphiboles of andesites and dacites of both volcanoes were produced. At the final stage (a temperature decrease to 900–810 °С and ascent of melts to a depth of 3 km), only amphiboles of dacites of both volcanoes crystallized.