Mesozoic evolution of Northeast Asia and the collision of the okhotsk microcontinent

Abstract

Tectonic models of Northeast Japan generally involve the progressive subduction of the Paleo-pacific oceanic crust during the Mesozoic and collision of the Okhotsk microcontinent at the end of the Cretaceous with Eurasia. However, these models are not based on a precise knowledge of the overall structure and succession of deformations in the collision zone. Our survey leads us to propose structural maps and cross sections of the Hokkaido Central Belt and a tectonic description of each tectonic stage. It appears that at the end of the Jurassic, until the Early Cretaceous an important event of nappe emplacement occurred. We interprete this event as the collision of the Okhotsk block with Eurasia, much earlier than in classical models. During this collision, the oceanic crust of a marginal basin was obducted with an east vergence and partly metamorphosed. Contemporaneously with the collision, an important volcanism, linked with the Pacific subduction, started and continued during the whole of the Cretaceous period. The continental margin was affected by strike-slip faults running parallel to the margin with a left-lateral motion. The main fault was the Tanlu fault which accommodated the northward movement of the eastern part of the Asian continent which led to the closing of an oceanic domain between Siberia and the Okhotsk block. This tectonic scenario ended 70 m.y. ago contemporaneously with the cessation of the volcanism in the Okhotsk-Uda Margal volcanic belt. From the Eocene to the Middle Miocene a right-lateral strike-slip motion along Sakhalin and Hokkaido gave rise to the Hidaka shear zone and finally led to the opening of the Sea of Japan.