New Isotope-Geochemical Data on the Cenozoic Volcanism and the Geodynamics of the Underwater Vityaz Ridge (Pacific Slope of the Kuril Island Arc)

Original analytical data on trace elements and radiogenic Nd and Pb isotopes in the volcanic rocks of the Southern and southwestern part of the Northern plateaus of the underwater Vityaz Ridge are presented. Interpretation of these data and a comparison with published materials on the volcanic rocks from the southern and northern parts of the Kuril Island Arc (KIA), which formed on two basement blocks of different genetic nature, allow us to draw the following conclusions. The tholeiite varieties of volcanic rocks of the Southern Plateau and the southern part of the KIA have similar isotope-geochemical features, which point to the similar geodynamic conditions of the formation and the identical influence of low-temperature fluid on magma-generating processes. The geochemistry of the volcanic rocks of the Northern Plateau, which are mainly represented by subalkaline varieties, indicates a more pronounced contribution of the mantle component to the magmagenesis and a greater degree of influence of high-temperature melt compared to the rocks of the Southern Plateau, but a lesser degree compared to the rocks of the northern part of the arc. The volcanics of both plateaus are derivatives of a single mantle source, the MORB of the Indian Ocean (Indian MORB), and were formed together with the rocks of the southern part of the KIA within the lithospheric block transformed by tectonomagmatic processes that accompanied the opening of the Kuril Basin.