Late Mesozoic–Cenozoic Stages of Volcanism and Geodynamics of the Sea of Japan and Sea of Okhotsk

A model of the geological evolution of the Japan and Okhotsk seas was developed based on radioisotope age, mineralogical, and isotope-geochemical study of the Late Mesozoic–Cenozoic volcanic rocks. The geodynamic settings of volcanic stages were determined as follows: (1) the Late Cretaceous continental-margin (calc-alkaline), (2) the Eocene transform-margin (adakite) in the Sea of Okhotsk, (3) the Miocene–Pliocene marginal sea (alkaline basaltic) in the Sea of Japan, and (4) the Pliocene–Pleistocene island arc (calc-alkaline) in the southern Sea of Okhotsk. It has been established that parental magmas were derived from subcontinental lithosphere, oceanic asthenosphere, and lower-mantle plume-continental (CAB) and plume-oceanic (OIB) sources. Geodynamic settings changed from the Late Cretaceous subduction to the Maastrichtian–Pliocene transform margin. The transform margin setting involved destruction and extension, maximum oceanic-margin spreading (end of the Early Miocene–beginning of the Middle Miocene), and post-spreading lower mantle plume upwelling (the Middle Miocene – Pliocene). It was completed by the resumption of the Pliocene–Pleistocene subduction of the Pacific plate beneath the Eurasian continent.