Initiation of Subduction Beneath the Northeastern Asian Continent in the Late Cretaceous.

The Late Albian–Campanian Okhotsk–Chukotka Volcanic Belt (OCVB) extends along the northeastern Asian margin for more than 3000 km. Toward the Pacific, this belt adjoins the microcontinent of the Sea of Okhotsk in the west and the Jurassic–Early Cretaceous terranes of the Northern Koryak region in the east. Various rock assemblages of these terranes are overlain by shallow-water and continental sediments coeval with the OCVB volcanic rocks. These sediments significantly differ from deposits of deep-water trenches and accretionary wedges suggesting location of the Late Cretaceous OCVP subduction zone southeast of the Koryak terranes. The Jurassic–Early Cretaceous Uda‒Murgal island arc (which was accreted in the Barremian) and the Late Albian–Campanian Okhotsk–Chukotka Volcanic Belt, which are two major subduction-related structures of the northeastern active margin of Asia, were originated with the interval of 20 Ma (Late Barremian–Aptian–Early Albian). During this time interval the Jurassic–Late Cretaceous North Koryak complexes of various geodynamic affinities were juxtaposed, transported and accreted to the Asian continent in a local area restricted by the Siberian continent and the Chukotka continental block (Hauterivian–Early Barremian). The data presented in this paper contradict the hypothesis of the North Koryak terranes having been formed within the Pacific oceanic plates. It is proposed that these terranes composed of rock complexes of various geodynamic settings were originated in the Late Mesozoic eastern part of the Mongol-Okhotsk Ocean. The chaotic transformation and movement of the Northern Koryak terranes were probably related to escape tectonics during the closure of the Mongol–Okhotsk Ocean, which resulted from collision of the Amur block of the Sino-Korean craton with the Siberian continent. [ABSTRACT FROM AUTHOR]