1. Introduction The eastern margin of the Eurasian Continent, since Cretaceous, became an Andean type volcanic belt, which was related to subduction of oceanic plates (Takahashi, 1991; Zonenshain et al., 1990). The volcanic activity con- tinued into the Paleogene and produced large amounts of calc-alkaline volcanic and plutonic rocks. The original form of the volcanic belt has been modified by crustal deformations with formations of marginal seas and colli- sions of continents and their fragments, and lost its origi- nal shape (e.g., Faure and Natal’in, 1992). Paleomagnetic reconstructions of the Japanese Islands have revealed that the opening of the Japan Sea occurred during the Early to Middle Miocene, and that, before the opening, the Japanese Islands were situated along Sikhote Alin and the Korean Peninsula as marginal parts of the Eurasian continent (Otofuji and Matsuda, 1983; Otofuji et al., 1985; Otofuji and Matsuda, 1987). How- ever, detailed areal distribution and formation ages of the igneous rocks as well as such reconstruction of the east- ern part of the Eurasian continent are required to build up a plausible model for the magma genesis, mineralization, and tectonic setting. Sato et al. (1993b) and Ishihara et al. (1997) pointed out that the granitoids and related ore deposits in Sikhote Alin resemble to those of the Sanyo belt, Southwest Japan, in their Cretaceous ages, magnetic properties of the ilmenite-series and type of ore deposits. However, from the southeastern part of Sikhote Alin were reported Pale- ogene radiometric ages (e.g., Baskina and Volchanskaya, 1972; Ishihara et al., 1997) and magnetite-series grani- toids (Sato et al., 1993a) which are the features of the igneous rocks of the San’in belt in Southwest Japan. In this paper, we present new zircon fission-track ages and magnetic susceptibilities of the Cretaceous to Paleo- gene volcanic rocks from the southeastern part of Sikhote Alin, and try to correlate them to those of the Japanese Islands. 2. General Geology of Sikhote Alin Sikhote Alin is underlain mainly by the Precambrian Khanka Massif, Late Paleozoic to Mesozoic complexes, and Cretaceous to Paleogene igneous rocks (Natal’in, 1993; Khanchuk et al., 1996) (Fig. 1). The Late Paleozoic Fission-track Ages and Magnetic Susceptibility of Cretaceous to Paleogene Volcanic Rocks in Southeastern Sikhote Alin, Far East Russia Takaaki MATSUDA * 1 , Tohru SAKIYAMA * 2 , Ryo ENAMI * 3 , Yo-ichiro OTOFUJI * 3 , Vladimir G. SAKHNO * 4 , Anatoly P. MATUNIN * 4 , Ruslan G. KULINICH * 5 and Petr S. ZIMIN * 5 Abstract: Seven zircon fission-track ages and 30 magnetic susceptibilities were measured on welded pyroclastic rocks from the Bogopol and Sijanov Groups of the Cretaceous to Paleogene volcanic rocks in the southeastern part of the eastern Sikhote Alin volcano-plutonic belt, Far East Russia. The fission-track ages range from 42.7 Ma to 64.0 Ma which indicate that both the groups are of Early Paleogene time. Two thirds of the samples from the Bogopol Group have high magnetic susceptibili- ty values, more than 3 × 10 -3 SI unit, which imply that they are of the magnetite-series, whereas the samples from the Sijanov Group show 3 × 10 -3 to 8 × 10 -5 SI unit which suggest this group of probably the ilmenite-series. The Paleogene age and high magnetic susceptibility of the Bogopol Group are quite similar to the Paleogene igneous rocks of the San’in belt, Southwest Japan. This suggests, taking accounts of the opening of the Japan Sea, that the eastern Sikhote Alin volcano-plutonic belt continued to the San’in Belt, and that the Paleogene igneous rocks along the Japan Sea coast of North- east Japan were situated along the volcanic front of the eastern Sikhote Alin volcano-plutonic belt. Received on September 24, 1998, accepted on December 15, 1998 * 1 Department of Geology, Faculty of Science, Himeji Insti- tute of Technology, Shosha 2167, Himeji 671-2201, Japan [e-mail: matsuda@sci.himeji-tech.ac.jp] * 2 Institute of Natural and Environmental Sciences, Himeji Institute of Technology, Yayoiga-oka, Sanda 669-1546, Japan * 3 Department of Earth and Planetary Science, Faculty of Science, Kobe University, Rokkodai-chou 1-1, Nada-ku, Kobe 657-0013, Japan * 4 Russian Academy of Science, Far East Geological Insti- tute, Vladivostok, Russia * 5 Russian Academy of Science, Pacific Oceanological Insti- tute, Vladivostok, Russia Keywords: Sikhote Alin, Cretaceous to Paleogene volcanic rocks, fission-track age, magnetic susceptibility RESOURCE GEOLOGY, vol. 48, no. 4, 285–290 1998 285