Search

The results of comprehensive petrological, geochemical, and mineralogical studies of effusive volcanic rocks from the diamond-bearing Tolbachik fissure eruption of 2012-2013 (TTI-50) are summarized. It is concluded that the eruption was two-phase, which began with a short-term eruption of trachybasalts and continued with the formation of trachyandesite basalts. In comparison with lavas from other Tolbachik eruptions (BTTI, BD), the studied volcanic rocks are characterized by higher alkalinity and high K content (up to shoshonites), but lower Mg content. In terms of geochemical properties, they correspond to riftogenic magmatites formed due to the deep-mantle chamber of picrite magma. The studied volcanic rocks are characterized by widely varying vesicularity up to bubbly lavas, which comprise 80-90% of volcanic glass, and whose degree of recrystallization varies from maximum in basaltic trachyandesite to minimum in trachyandesitebasalt bomb. According to the degree of iron oxidation in the glass phase, volcanics correspond to the products of terrestrial eruptions in an island-arc or continental-rift geodynamic setting. The microlites are dominated by olivine Fo56-84, plagioclases An87±9 Ab9±10 Ort4±2, and spinel solid solutions based on magnetite, magnoferrite, ulvite, and cuprospinel. Individuals of decomposition in phase-heterogeneous grains of magnetite are represented by hemoilmenite and ilmenite. As accessory microminerals, jirite-spionkopite of composition Cu1.7S-Cu1.32S, native iron composed of Fe75Sn4(Cu,Mn,Cr), and native copper of composition Cu7-10(Sn0.9-1.8Fe0.1-0.2)1-2