Geochemistry and Petrogenesis of Volcanic Rocks in the Kuril Island Arc

Newly obtained precise analytical data on trace elements and radiogenic Sr, Nd, and Pb isotopes testify to anomalous geochemical characteristics of mafic and intermediate Quaternary lavas in Paramushir (in the north of the Kuril arc), Kunashir and Iturup (in the south) islands, which are the largest three islands of the Kuril island arc. The high K and LREE concentrations in the volcanic products in Paramushir Island resulted from the southward expansion of the mantle thermal anomaly of the Kamchatka Peninsula and the involvement of melts related to the melting of oceanic sediments in magma generation. The depleted characteristics of the mafic volcanics are explained by the relatively young tectono-magmatic events during the opening of the Kuril backarc basin. The Kuril island-arc system developed on a heterogeneous basement. The northern islands are a continuation of the volcanic structures of southern Kamchatka, which were formed above an isotopically depleted and hot lithospheric mantle domain of composition close to that of the Pacific MORB type. The southern islands were produced above an isotopically enriched and cold lithospheric domain of the Indian-Ocean MORB type, which was modified in relation to relatively young backarc tectono-magmatic processes. Although issues related to the genesis of the transverse geochemical zoning were beyond the originally formulated scope of our research, the homogeneous enough isotopic composition of the rear-arc lavas in the absence of any mineralogical and geochemical lines of evidence of crustal contamination suggests an independent magmatic source.