The article presents new petrogeochemical data on the Middle Miocene-Pliocene volcanic rocks from central part of Iturup Island (Great Kurile Chain). It is shown that volcanism of the Middle Miocene-Early Pliocene age in the central part of the Iturup Island took place in a suprasubduction setting. The distribution of high field strength elements (HFSE) and their ratio in the basaltoids indicate their formation upon partial melting of the depleted upper mantle, while the enrichment of rocks with large ionic lithophilic elements (LILE) indicates both a fluid mantle additive introduced into the melts during the evolution of primary magma and the participation of a low-temperature suprasubduction fluid. The established differences in the composition of the basaltoids of the frontal and rear zones due to the limited number of analyzed samples are considered preliminary. Thus, basaltoids in the rear zone are distinguished by higher concentrations of Th, Pb, HFSE (Nb, Zr, Y, Hf), relative enrichment in LREE, pronounced negative Zr and Hf anomalies, and positive Eu.

The article presents the first study of isotopic and geochemical composition of Late Cretaceous - Early Paleogene kitilgin high-potassium volcanic rocks from the Valaginsky Range, Kamchatka. Mineralogic and chemistry composition as well as radiogenic isotope ratios of rocks show that they are similar to kirganik shoshonites from the Sredinny Range, Kamchatka. Low HFSE composition respectively to MORB composition, low 87Sr/86Sr and high 143Nd/144Nd suggest that melts were formed from MORB-like mantle. Rocks enriched with LILE give evidence for fluid mantle admix caused by initial magma evolution.