Opening of the Japan Sea

In recent years, many hydrothermal solution venting and sulfide-sulfate precipitations have been discovered on the seafloor of back-arc basins and island arcs (e.g., Ishibashi and Urabe, 1995) (section 2.3). Therefore, it is widely accepted that the most Kuroko deposits have formed at back-arc basin, related to the rapid opening of the Japan Sea (Horikoshi, 1990). 

Lallemand and Jolivet (1986) have interpreted the opening of the Japan Sea as a pull-apart basin between two right-lateral strike-slip fault zones the Yagsan-Tsushima fault to the west and the Tartary-Hidaka shear zone to the east. 

Although many discussions on the origin of the Japan Sea have been carried out since the pioneer works by Tokuda (1927), and Terada (1934) who considered that the Japan Sea formed by southward migration from the Asian continent, the problem of the mechanism of the opening of the Japan Sea remains unsolved as mentioned above. 

Kuroko formation occurred at middle Miocene (15-16 Ma). But the opening of Southwest and Northeast Japan Sea occurred probably from the age earlier than this age. Therefore, it is thought that the beginning of the opening of the Japan Sea did not directly relate to the Kuroko formation. 

As mentioned above, formation of back-arc basins and marginal seas may be important for the formation of Kuroko and vein-type deposits, although genetic relationship between Kuroko formation and opening of the Japan Sea is not clear. For example, Horikoshi (1977) insists that vein-type deposits in Northeast Hokkaido did not form without the opening of Ohotsuku back-arc basin. 

In contrast to Southwest Japan, opening of northeastern part of the Japan Sea is unclear, compared with the southwestern part of Japan. Tosha and Hamano (1988) made a paleomagnetic study of Tertiary rocks of Oga Peninsula (northern Honshu) and considered that a counterclockwise rotation of Northeast Japan with respect to eastern Asia took place between about 22 Ma and 15 Ma and the before the rotation. Northeast Japan was situated along the east coast of the Asian continent. 

Otofuji (1996) proposed a double door opening mode with a fast spreading rate of 21 cm/year for the evolution of the Japan Sea, caused by the injection of asthenosphere with a low viscosity beneath the Japan Sea area. 

Tamaki, K. (1995) Opening tectonics of the Japan Sea. In Taylor, B. (ed.), Backarc Basins Tectonics and Magmatism, Plenum Publ., pp. 407-420. 

Tatsumi, Y., Maruyama, S. and Nohda, S. (1990) Mechanism of back arc opening in the Japan sea role of asthenospheric injection. Tectonophysics, 181, 299-306. 

Horikoshi, E. (1990) Opening of the sea of Japan and Kuroko deposit formation. Mineralium Deposita, 25, 140-145. 

Otofuji, Y, Hashida, A. and Torii, M. (1987) When was the Japan Sea opened. Paleomagnetic evidence from southwest Japan. In Nasu, N. et al. (eds.). Formation of Active Ocean Margins. D. Reidel Publ., pp. 551-566. 

PFOS has also moved deeper in the oceans. In one study between 2002 and 2006, a team of researchers collected samples from 62 locations offshore of Japan and Angola and in the open ocean at various depths [53]. These open-water sampling locations were in the North Atlantic Ocean, Mid-Atlantic Ocean, central to western Pacific Ocean, soufh Pacific Ocean, South China Sea, Japan Sea, and Indian Ocean. The research team concluded that the distributions of PFOS and fhe relafed compound perfluorooctanoate (PFOA), laferally and verfically, were consistent with transport via the Great Ocean Conveyer Belt. The relatively low density distribution of samples and the relatively short period of use of PFOS (about 50 years) make it difficult to reach a definitive conclusion, but the results suggest, in the researchers view, the potential for global fhree-dimensional transport of persistent compounds. 

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