Collision, Rotation, and Back-Arc Spreading in the Region of the Okhotsk and Japan Seas

The India-Eurasia collision caused extensive deformation in the Eurasia Continent since late Eocene time. We propose that back-arc spreading in the Okhotsk and Japan Seas was related to the movement of microplates relevant to the India-Eurasia collision. The Kuril Basin of the Okhotsk Sea and the basins of the Japan Sea were formed as back-arc basins simultaneously. Their late Oligocene to middle Miocene age is constrained by sediment stratigraphy, basement depth, and heat flow data. The movements of two microplates, the Okhotsk and Amuria Plates, are significant for the tectonics of the Okhotsk and Japan Seas. Simultaneous retreat of both microplates from trench hinge lines caused back-arc spreading in the Kuril Basin and the Japan Sea. The Amuria Plate moved north-northeastward due to the India-Eurasia collision. This caused pull-apart opening of the Baikal Rift along a transform boundary between the Siberia and Amuria Plates and a collision along the Stanovoy Range at its northern margin. This movement triggered a clockwise rotation of the Okhotsk Plate with a component of dextral collision between the Okhotsk and Amuria Plates, which is well observed along the central zone of the Sakhalin-Hokkaido islands between the two back-arc plates. The clockwise rotation of the Okhotsk Plate is suggested by the southwestward fan-shaped opening of the Kuril Basin. The Kuril Basin narrows to the northeast and terminates south of the Kamchatka Peninsula, where a relative rotation pole between the Okhotsk and Kuril forearc plates is located. The Kamchatka Peninsula was a zone of collision on the other side of the clockwise rotating Okhotsk Plate during the opening of the Kuril Basin. The Sredinny Range in the Kamchatka Peninsula is one of the results of the collision between the Okhotsk Plate and the forearc plate of the Kuril Arc. The bending of the Japanese islands occurred in association with the back-arc spreading of the Yamato Basin of the Japan Sea.