The petrogenesis of rocks of the Ostryi and Ploskii volcanoes and the relationship between volcanic occurrences of basaltic and trachybasaltic magmas in the Tolbachik Dol area, Kamchatka

Abstract

We developed a petrologic and geodynamic model for the magma generation of volcanic formations in the Tolbachik Dol area. Differences have been found in the evolution of volcanic ejecta and the mineral composition of rocks on Ostryi and Ploskii Tolbachik stratovolcanoes on the one hand and in that of the regional zone of cinder cones on the other. We conclude that the basaltic and the trachybasaltic magmas were generated independently of each other and that these magmas were mixed during the time when central volcanism was giving way to fissure volcanism. The leading process that was responsible for the generation of basaltic and trachybasaltic series was crystallization differentiation, while the compositional variation in the stratovolcano and cinder rocks can be explained by the supply of an alkaline component into the basaltic magma chamber and subsequent accumulation during magma crystallization.