Evolution of rock compositions observed during the 2012-2013 New Tolbachik Volcanoes eruptions - online mantle control
The paper presents new isotope geochemical data on volcanic rocks from the New Tolbachik fissure eruption (NTFE-50). These data were compared with those on the volcanic rock compositions from the 1975-76 Great Tolbachik fissure eruption (GTFE) and the Klyuchevskaya group of volcanoes (KGV). Two petro-geochemical evolution trends of volcanic rocks compositions have been revealed: calc-alkaline for island-arc-type rocks and subalkaline for intraplate-type rocks. The first trend is characterized by different degrees of lithosphere source melting followed by magma melts fractionatiom. The second trend reflects the results of melt mixing formed at during the enriched lithosphere mantle melting, on the one hand, and the fluid-melt component of the mantle diapir, on the other hand. During NTFE-50 the transition from the first cycle basaltic andesites to basalts of the following cycle was accompanied by the increase in MgO, Ni, Rb, V, Ti, Y, La, Sr concentrations, increase in 208Pb/ 204Pb and La/Yb ratios, but decrease in SiO 2, Pb, Nb, Zr, Hf contents and Sr-isotope ratios that probably could be explained by the increase of the melting degree of the lithosphere mantle reservoir. The basalt composition from NTFE-50 changed at the final stage of eruption followed by the increase in almost all fluid- and melt-mobile elements contents at minor changes in MgO and Ni contents. It could be explained by the processes of the melts mixing, resulted from the lithosphere and asthenosphere mantle sources melting.