BREAKUP OF THE LATE CRETACEOUS ACHAIVAYAM-VALAGIN VOLCANIC ARC IN THE PALEOCENE (TERRANES OF SOUTHERN KORYAKIA AND EASTERN KAMCHATKA)

Abstract

The origin and evolution of the Late Cretaceous and Late Cretaceous–Paleogene island arcs, which make up accreted terranes in the present-day structure of southern Koryakia and eastern Kamchatka, have actively been discussed in publications for the past 15 years. Principal debatable points mainly concerned kinematics of the dislocation of terranes prior to their accretion. Island-arc terranes of southern Koryakia and eastern Kamchatka were regarded as remains of ensimatic island arcs transported over considerable distances. It was believed that the Late Cretaceous Achaivayam–Valagin and the Late Cretaceous–Paleogene Kronotskii and Govena arcs started to form in the Late Cretaceous at close paleolatitudes of the Pacific. It was customary to assume that subduction zones under the Late Cretaceous Achaivayam–Valagin and Late Cretaceous–Paleogene Kronotskii and Govena arcs were oppositely directed. The causes of such an unusual phenomenon, which has no analogues in the present-day geodynamic setting in the western Pacific, and the geological substantiation of such a paleotectonic situation have not been considered so far.