Granitoids in the basement of the Kurile island arc system

Abstract

The Kurile island arc system consists of three large structural elements: the frontal zone, the Greater Kurile Ridge, and the backrc zone adjacent to the latter on the side of the Sea of Okhotsk in the form of submarine volcanic ridges. The frontal zone includes the Pacific slope of the Kurile arc consisting of the underwater Vityaz Ridge and islands of the Lesser Kurile Ridge. It touches the Pacific Plate, and the sea bottom in this area hosts outcrops of the basement of the entire island system. The data on the composition and age of the basement are of importance for solving the problem of the origin of the island arc, since they allow the onset of its formation and evolution to be reconstructed. The evidence for interpreting the composition of the basement beneath the Greater Kurile Ridge was provided only by single finds of metamorphic and intrusive rocks occurring in the form of xenoliths in lavas of the Kurile Islands (1). Based on these findings, Sergeev (2) assumed the presence of the Hercynian or Mesozoic folded basement under this structure, while Vasil'ev (3) believes that the entire island block and Vityaz Ridge represent constituents of the folded domain formed at terminal stages of the Mesozoic orogeny.