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

本文通过对俄罗斯远东Sikhote Alin地区白垩系至古近系火成岩的调查，探讨了日本列岛从欧亚大陆漂移而形成日本海的详细模式以及欧亚大陆东部在日本海打开过程中的变形。采集了约45个火山岩测年、古地磁测量和岩石学研究地点的岩石样品，以及25个花岗岩测年和岩石学研究地点的岩石样品。在火山岩上测定了40个锆石和11个磷灰石裂变径迹年龄。尽管火成岩活动的年代被认为主要发生在晚白垩世，但大多数年龄表明火成岩活动发生在古近纪。年龄与同一火山群的黑云母K-Ar年龄一致。类似的古近系火成岩分布在日本东北部日本海沿岸。这些火成岩形成于日本海打开之前的火山带。对锡霍特山脉上部火山岩的古地磁测量表明，古近系火山岩的走向与构成欧亚大陆东部地块的走向一致。这表明欧亚大陆东部自古近纪以来一直是一个连贯块体，在日本海打开阶段没有发生变形。火山岩下部的古地磁方向表明，锡霍特阿林地区在地理上被划分为5个区域，并经历了相对旋转。相对块体旋转停止，直至52.6Ma时上部火山岩形成。

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.