Radioactive elements in volcanites from island arcs of the West Pacific active margin

Data on the radioactive element concentration and their ratio in volcanites of Lau and Tonga, Mariana and Kyushu-Palau, Kuril-Kamchatka and Japanese volcanic arcs show that volcanites of arcs, originated on the oceanic type crust, are characterized by high K/U ratio, (2-10)x104. Volcanites of arcs with the well developed continental crust (Japanese and New-Zealand arcs) have 1x104 ratio. High K/U ratio in volcanites of Kuril-Kamchatka island arc with oceanic type crust indicates epioceanic nature of this structure. Highly metamorphic magmatic rocks and sediments of the ancient oceanic crust, and not the mantle substrate, appear to be the source of island-arc magmas with typical high K/U ratio more, than 2x104