Rifting Process of Eastern Margin of Eurasia Continent-Comparison of post-Jurassic between Sikhote Alin and Japan Islands-

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We surveied the Cretaceous to Paleogene igneous rocks in the Sikhote Alin area, Far East Russia to investigate the detail mode of the opening of the Japan Sea with drifting of the Japan Islands from the Eurasia continent and of the deformation of the eastern parts of the Eurasia continent during the opening of the Japan Sea. Rock samples were collected from about 45 sites of volcanic rocks for radiometric dating, paleomagnetic measurement and petrological study, and from 25 sites of granitic rocks for radiometric dating and petrological study.40 zircon and 11 apatite fission track ages were measured on the volcanic rocks. Most of the ages show that the igneous activity occurred in Paleogene, although the age of the igneous activity had been considered to be mostly in the Late Cretaceous. The ages coincide with the biotite K-Ar ages from the same volcanic group. Similar Paleogene igneous rocks are distributed along the Japan Sea coast of the Northeast Japan. these igneous rocks were formed in a volcanic belt before the opening of the Japan Sea.Paleomagnetic measurements of the upper parts of the volcanic rocks in the Sikhote Alin show tht the directions of the Paleogene volcanic rocks coincide with those of the massifs which made up of the eastern parts of the Eurasia continents. This implies that the eastern parts of the Eurasia continents have been a cohirent block from the Paleogene and did not deformed during the opening stage of the Japan Sea. Paleomgnetic directions of the lower parts of the volcanic rocks imply that the Sikhote Alin area was geographically divided into five areas, which underwent relative rotation each other. The relative block rotation has ceased until 52.6Ma when the upper parts of the volcanic rocks formed.