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Volume 57 (2003)
- Issue 6 Pages 333-
- Issue 5 Pages 253-
- Issue 4 Pages 173-
- Issue 3 Pages 95-
- Issue 1-2 Pages 1-
Volume 57, Issue 6
Displaying 1-5 of 5 articles from this issue
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Gentaro KAWAKAMI, Makoto KAWAMURAArticle type: Article
2003 Volume 57 Issue 6 Pages 333-342
Published: November 25, 2003
Released on J-STAGE: July 14, 2017
JOURNAL OPEN ACCESSUp-to-date interpretation of orogenic processes associated with arc-arc collision during Miocene time in central Hokkaido is proposed through reconsiderations on stratigraphic evidence. Thermo-chronological studies of the Hidaka Metamorphic Belt in last decade revealed a rapid uplifting of fold-and-thrust belt during latest Early to early Middle Miocene time. Spatio-temporal development of the Tertiary System and their sedimentologic features clarify the onset of foreland basin evolution synchronous with such rapid uplifting in fold-and-thrust belt. The transverse geometry of foreland-forebulge system is well restored along the section from the Yubari Mountains to Umaoi Hills area. Although recent geophysical investigations provide the image of deep-crustal structure beneath the collision zone in central Hokkaido, its geological interpretation have been yet insufficient. Stratigraphic and sedimentologic analyses of foreland basin-fill will provide relevant interpretation of evolutional processes not only in surficial, but also deep crustal structures of central Hokkaido.View full abstractDownload PDF (2218K) -
Ayumu NOJO, Takuya ITAKI, Toyoho ISHIMURAArticle type: Article
2003 Volume 57 Issue 6 Pages 343-355
Published: November 25, 2003
Released on J-STAGE: July 14, 2017
JOURNAL OPEN ACCESS'The Regional Geology of Japan-Part 1 Hokkaido' published in 1990, which encompasses geology of Hokkaido, has been providing general, useful information about Cenozoic lithostratigraphy and chronology as well as the other rocks and strata of older ages. After the publication of the book, numerous microbiostratigraphic data have added new imformation to the Cenozoic stratigraphy of Hokkaido and its surrounding sea. This resulted in improvements in dating of formations and stimulated redefinition of many lithostratigraphic units. We compile such biostratigraphic studies and present bibliographic tables and figures. Further discussion is summarized as follows: 1) Because there are a few studies of cores from submarine deposits around Hokkaido, the correlation between land and marine deposits remains insufficient. More detailed investigations and correlations of Cenozoic deposits both in land and peripheral sea of Hokkaido may lead to further understanding about the geological backgrounds of northern Japan. 2) Many of those previously published studies used diatom for age-determination, but only a few used the other microfossil groups. Biostratigraphic studies using two or more micro fossil groups should be prompted in order to determine the age of Cenozoic formations of Hokkaido more precisely.View full abstractDownload PDF (2094K) -
Akihiko SUZUKIArticle type: Article
2003 Volume 57 Issue 6 Pages 357-364
Published: November 25, 2003
Released on J-STAGE: July 14, 2017
JOURNAL OPEN ACCESSTertiary molluscan faunas of the Okhotsk Sea borderland in Hokkaido are divided mainly into five phases in ascending order, the Tatsukobu-Tsubetsu, Takinoue, Lower Togeshita, Upper Togeshita and Takikawa-Honbetsu Faunas, based on chronostratigraphic and paleontological data. The Tatsukobu-Tsubetsu Fauna (Stage I:30-20 Ma) is represented by cold-water elements and lack of warm-water elements. The fauna is presumed to lived under the temperate conditions, and belongs to the so-called Acilana tokunagai Fauna. The Takinoue Fauna (Stage II:16.5-15 Ma) is characterized by mixture of warm- and cold-water elements, but lack of subtropical taxa. The fauna and the Chikubetsu Fauna at the same age are presumed to have lived in the temperate realm. These faunas are correlated with the Kadonosawa Fauna of Honshu and are corresponded to the Mid-Neogene Climatic Optimum. The Lower Togeshita Fauna (Stage III:14-10 Ma) is dominated by cold-water elements and is presumed to have lived in mild- to cool-temperate realm. The Upper Togeshita Fauna (Stage IV:10-6 Ma), including deep-water elements, lived in mild-temperate one. Theses faunas are correlated with the Lower and the Upper Shiobara-Yama Faunas of Honshu respectively. The Takikawa-Honbetsu Fauna (Stage V:6-2 Ma), characterized by Fortipecten takahashii, is dominated by cold-water species. The fauna flourished under cool-temperate conditions. The faunal change mentioned above is presumably controlled by global and local environmental changes which might have occurred in the Okhotsk Sea borderland of Hokkaido throughout the Tertiary age.View full abstractDownload PDF (1286K) -
Satoshi OKAMURAArticle type: Article
2003 Volume 57 Issue 6 Pages 365-373
Published: November 25, 2003
Released on J-STAGE: July 14, 2017
JOURNAL OPEN ACCESSThe Cenozoic volcanic rocks in Hokkaido record a tectonic transition from continental margin to island arc in connection with the formation of the Japan Sea and the Okhotsk Sea. The temporal geochemical trends in volcanic rocks from west Hokkaido, Sikhote-Alin and Sakhalin suggest that there was a change in magma source from the enriched continental lithosphere to the depleted asthenosphere as the back arc basin opening progressed. It is likely that the Japan Sea opening and associated magmatism in the back-arc basin were triggered by lateral migration of the enriched asthenospheric mantle from the beneath northeast China toward the Japan arc. The Cenozoic volcanic rocks from Central - East Hokkaido include icelandite, high-Ti andesite and adakite. Geochemical feature of the icelandite closely associated with the high-Ti andesite suggests that the sources of the unusual arc-magmas are similar to the enriched continental lithosphere of Sikhote-Alin and Sakhalin. The adakite, which can be produced by slab melting at garnet stability field, may have a close association with an upwelling hot mantle. Several hypotheses have been put forward to explain the time of Kuril basin opening. Owing to a lack of geological data from the Kuril basin, genetic relationship between Cenozoic volcanism and the Kuril basin still remains unsolved.View full abstractDownload PDF (1302K) -
Takafumi OZAWA, Makoto SUGAWARA, Satoshi OKAMURA, Katsuhiko FURUYAMAArticle type: Article
2003 Volume 57 Issue 6 Pages 375-389
Published: November 25, 2003
Released on J-STAGE: July 14, 2017
JOURNAL OPEN ACCESSK-Ar age and chemical compositions of the volcanic rocks from the Toyono Formation have been determined to clarify the tectono-magmatic evolution during middle Miocene in the north Hokkaido, Japan. It mainly consists of andesitic to dacitic block and ash flow deposits and massive lava. The andesite lava gives an age of 11.77±0.26 Ma. This age indicates that the volcanism forms a part of the volcanic activity taking place from 14 to 9 Ma in the north Hokkaido. The rocks of the Toyono Formation are distinct from the surrounding Miocene volcanic rocks and indicate adakite-like characteristics; high Sr/Y ratios, low Y contents, and depleted isotopic ratios (low ^<87>Sr/^<86>Sr and high ^<143>Nd/^<144>Nd), which can be produced by slab melting or lower crustal melting at garnet stability field. In addition, the rocks have high Mg, Ni contents, and high-Mg pyroxene phenocrysts. This may indicate that the rocks from the Toyono Formation have been produced by slab melting and subsequent interaction between the magma and the ultramafic rocks in the wedge mantle.View full abstractDownload PDF (1685K)
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