Studies of melt inclusions in minerals of some Kamchatka volcanoes are reported. We studies andesite basalts and andesites in volcanoes situated in the Central Kamchatka Depression (Shiveluch and Bezymyannyi) and in the East Kamchatka Volcanic Belt (Avacha and Karymskii). In addition, we studied the basalts of the 1996 eruption in the Karymskii Volcanic Center and the dacites on Dikiy Greben Volcano, southern Kamchatka. We used homogenization of melt inclusions and the analysis of chilled glass in these inclusions with electron and ion microlog sondes. More than 200 melt inclusions have been studied in minerals from 25 volcanic rock samples. It was found that the compositions of melt inclusions in andesite phenocrysts strongly vary in basicity; the content of SiO 2 varies between 56 and 80% wt, increasing silica percentage going along with decreasing concentrations of Al2O3, FeO, MgO, CaO and increasing concentrations of Na2O and K2O. Most (about 80%) of glass in the inclusions have dacite and rhyolite compositions. However, the compositions of acid melts (SiO2 > 65% wt) which produce the andesites are significantly different from those which produce the dacites and rhyolites as to the content of TiO2, FeO, MgO, CaO and K2O. Comparison between the compositions of melt inclusions from andesite plagioclase on the four volcanoes showed considerable differences. The basic andesites (56-59% SiO2) of Bezymyannyi Volcano exhibit a large scatter in inclusion composition (SiO2 = = 56-81%). The more acid andesites (SiO2 = 61%) of Shiveluch Volcano show a lower scatter in inclusion composition (SiO2 = 67-79%). The melt inclusions in the Karymskii andesites are amore basic. They are enriched with Fe, Ti, Ca, Mg, P, Na and are considerably depleted in K. The melts that produce the Karymskii andesites are probably less differentiated. On the volcanoes under study we also found high-potassium melts (K 2O = 3.8-6.8% wt), independent of the concentrations of SiO2 in them (the range here is between 51.4 and 77.2% wt). The melts differ considerably between volcanoes as to the concentration of volatiles. The greatest concentrations of H2O are found in the Shiveluch melts (3.0 to 7.2% wt with the mean equal to 4.7% wt) and on Avacha (4.7-4.8% wt), lower concentrations being in the melts of Dikiy Greben (0.4-1.8% wt) and Bezymyanyi (<1% wt). Using fluid inclusions of CO2 found in andesite plagioclase of Shiveluch Volcano, we inferred a pressure of 350-1600 bars, which corresponds to the depth of the magma chamber equal to 1.5-6 km. We found the concentrations of 17 admixture elements in glass of melt inclusions sampled from the plagioclase of four volcanoes (Avacha, Bezymyannyi, Dikiy Greben, Shiveluch). Judging by the concentrations of these elements, the melts here studied are similar to the typical island arc magmas.

Восстановлена история формирования вулкана. Динамика его активности реконст­руирована в соответствии с абсолютной хронологической шкалой. Показано, что вулка­ническая активность имела пульсационный характер. Каждый период активизации ха­рактеризуется закономерной сменой состава вулканитов. Возраст собственно стратовулкана Безымянный составил около 5500 лет. Датированы крупнейшие пирокластические извержения. Подсчитан объем продуктов и средняя интенсивность выноса вещества за время жизни вулкана. Отмечено резкое возрастание интенсивности выноса вещества на современном этапе. Анализ реконструированной истории вулкана позволяет полагать, что его активность сохранится в ближайшие 200—300 лет.