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

通过对俄罗斯远东Sikhote Alin地区白垩纪至古近纪火成岩的测量，探讨了日本海开放过程中日本列岛从欧亚大陆漂移的详细模式，以及日本海开放过程中欧亚大陆东部的变形模式。对45个火山岩点和25个花岗质岩点的岩石样品进行了放射性测年、古地磁测量和岩石学研究，测定了40个锆石和11个磷灰石裂变径迹年龄。以往认为的岩浆活动时代主要在晚白垩世，但大多数时代表明岩浆活动发生在早第三纪。其年龄与同一火山岩群的黑云母K-Ar年龄一致。类似的古近纪火成岩分布在日本东北部的日本海沿岸沿着。对锡霍特阿林火山岩上部的古地磁测量表明，古近纪火山岩的方向与欧亚大陆东部的火山岩方向一致。这表明欧亚大陆东部自古近纪以来一直是一个同向陆块，在日本海开启阶段没有发生变形。火山岩下部的古地磁方向表明，Sikhote Alin地区在地理上可分为五个区域，这些区域相互经历了相对旋转。相对块体旋转停止至52.6Ma火山岩上部形成。

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.