Tectonics of eastern margin of the Asian continent

We carried out our paleomagnetic study in Kitakami massif in Northeast Japan，Nohi area in easternpart of Southwest Japan，and Sikhote Alin mountain in Russia.Paleogene and early Cretaceous welded tuffs have been sampled from eleven sites at the Omoe Peninsula(39.6°N，142.0°E)in the Kitakami massif of northeast Japan for paleomagnetic study.Westerly declinations with shallow inclination are identified after tilt correction in the62~71 Ma Heizaki volcanics(D=283.5°，I=9.4°，αI D295 IIE D2=8.0°)and in the 114~119 Ma Harachiyama Formation(D=274.2°，I=-20.4°)。The shallow inclination indicates that the Kitakami massif was located in low latitude(5°±4°N)at 62~71 Ma。Taking into account a reference paleomagnetic pole of the Paleocene expected from Sikhote Alin，the Kitakami massif was translated northward over 25°in latitude since65 Ma。We conclude that the Kitakami massif was incorporated into Asian continent at some time between 30 Ma and 22 Ma before opening of the Japan Sea.We investig…More ate formation of the curvature of the Median Tectonic Line(MTL)in Southwest Japan。We carried out a paleomagnetic study in the Nohi area，north of the curved part of the MTL in the eastern part of Southwest Japan。Paleomagnetic data indicate that the Nohi area are experienced a clockwise rotation through more than 45°with respect to the Asian continent as a part of Southwest Japan but that the amount of rotation of the Nohi area is 23°smaller than that of the central part of Southwest Japan.A new model is developed to explain the tectonic rotation.At about15 Ma during the latest stage of the clockwise rotation of Southwest Japan associated with opening of the Japan Sea，the eastern end moved southward by more than 60 km along a lest-lateral strike-slip fault which comprised the present north-south segment of the MTL and the Akaishi Tectonic Line。We conclude that the curvature of the MTL is a composite of the 15 Ma strike-slip fault system and a small bend of the MTL associated with the small differential rotation of the Nohi area with respect to the central part of Southwest Japan。Less：Less

We carried out our paleomagnetic study in Kitakami massif in Northeast Japan, Nohi area in easternpart of Southwest Japan, and Sikhote Alin mountain in Russia.Paleogene and early Cretaceous welded tuffs have been sampled from eleven sites at the Omoe Peninsula(39.6°N,142.0°E) in the Kitakami massif of northeast Japan for paleomagnetic study. Westerly declinations with shallow inclination are identified after tilt correction in the 62〜71 Ma Heizaki volcanics(D=283.5°,I=9.4°, αィイD295ィエD2=8.0°) and in the 114〜119 Ma Harachiyama Formation(D=274.2°, I=-20.4°). The shallow inclination indicates that the Kitakami massif was located in low latitude(5°±4°N) at 62〜71 Ma. Taking into account a reference paleomagnetic pole of the Paleocene expected from Sikhote Alin, the Kitakami massif was translated northward over 25° in latitude since 65 Ma. We conclude that the Kitakami massif was incorporated into Asian continent at some time between 30 Ma and 22 Ma before opening of the Japan Sea.We investig … More ate formation of the curvature of the Median Tectonic Line (MTL) in Southwest Japan. we carried out a paleomagnetic study in the Nohi area, north of the curved part of the MTL in the eastern part of Southwest Japan. Paleomagnetic data indicate that the Nohi area are experienced a clockwise rotation through more than 45° with respect to the Asian continent as a part of Southwest Japan but that the amount of rotation of the Nohi area is 23°smaller than that of the central part of Southwest Japan. A new model is developed to explain the tectonic rotation. At about 15 Ma during the latest stage of the clockwise rotation of Southwest Japan associated with opening of the Japan Sea, the eastern end moved southward by more than 60 km along a lest-lateral strike-slip fault which comprised the present north-south segment of the MTL and the Akaishi Tectonic Line. We conclude that the curvature of the MTL is a composite of the 15 Ma strike-slip fault system and a small bend of the MTL associated with the small differential rotation of the Nohi area with respect to the central part of Southwest Japan. Less