MELT INCLUSIONS IN MINERALS OF ALLIVALITES OF THE KURIL-KAMCHATKA ISLAND ARC

Abstract

The genesis of low-silica (generally olivine-anorthite) inclusions in volcanic rocks of the low-K tholeiitic island-arc series is a matter of active discussion. The study of melt inclusions in the major minerals of allivalites from three volcanoes of the Kuril-Kamchatka island arc proved the previously suggested genetic affinity between the allivalites and host lavas and the cumulative origin of these rocks. The composition of the parent melt was determined by two independent methods: by calculation and by temperature measurement during experiments. The temperature of coeval crystallization of olivine and plagioclase in allivalites is estimated at 1050-1100°C at an H 2O content of 1.5-2.0 wt % in the parent melt. Similar results were obtained for different volcanoes, which indicates a correspondence of the determined melt composition to the composition of the parent magma of low-K tholeiite for the Kuril-Kamchatka area. According to calculations, the formation of basaltic melt results from the separation of 7-8% of olivine-plagioclase cumulate from the parent magma.