The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
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Volume 110, Issue 9
Displaying 1-9 of 9 articles from this issue
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Articles
  • The strike-slip model: A synthesis on the origin and tectonic evolution of the Japanese Islands
    Jun-ichi Tazawa
    Article type: scientific monograph
    Subject area: Infomation Science
    2004 Volume 110 Issue 9 Pages 503-517
    Published: 2004
    Released on J-STAGE: January 07, 2005
    DOIhttps://doi.org/10.5575/geosoc.110.503
    JOURNAL FREE ACCESS
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    The tectonic development of the Japanese Islands are summarized in this article based on the strike-slip model. Pre-Neogene rocks of the Japanese Islands are divided into the following four terranes: (1) the South Kitakami Terrane (Early Ordovician to Late Devonian accretionary complex), (2) the Akiyoshi Terane (Middle to Late Permian accretionary complex), (3) the Mino Terrane (Early Jurassic to Early Cretaceous accretionary complex) and (4) the Shimanto Terrane (Late Cretaceous to Neogene accretionary complex). These terranes are arranged in a NE-SW direction, subparallel to the extension of the Japanese Islands, and younging towards the southeast, from the Japan Sea side to the Pacific side. Besides the four terranes, some nappes, (5) the Hida-Abukuma Nappe, consisting of the Palaeozoic and Mesozoic metamorphic rocks derived from the Qinling-Dabie Suture Zone, thrust over the terranes towards the east. The geotectonic framework of the Japanese Islands occurred through long-term subduction on the eastern North China margin since Early Ordovician. The terranes and nappes were moved and rearraneged by the Late Permian to Late Jurassic dextral strike-slip faulting, the Latest Jurassic to Earliest Cretaceous eastward thrusting, and the Early Cretaceous to Palaeogene (mainly Albian) sinistral strike-slip faulting. The total sinistral displacement during the Early Cretaceous to Palaeogene time is estimated to be 1500-2000 km. Finally, the rifting of the Proto-Japan from the Asian continent caused closkwise rotation of Southwest Japan and counterclockwise rotation of Northeast Japan in Early Neogene (Miocene). Furthermore, the collision of the Chishima (Kuril) Arc and the Izu-Ogasawara Arc caused the westward thrusting of central to eastern Hokkaido, and the deformation of the central part of the Honshu Arc, respectively.
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  • Bottom environmental changes during the past 100 years in Kitanada Bay, Ehime Prefecture, Southwest Japan
    Atsuko Amano, Takahiko Inoue, Naoya Iwamoto, Fujihiko Shioya, Yoshio I ...
    Article type: scientific monograph
    Subject area: Infomation Science
    2004 Volume 110 Issue 9 Pages 518-527
    Published: 2004
    Released on J-STAGE: January 07, 2005
    DOIhttps://doi.org/10.5575/geosoc.110.518
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    Bottom environmental changes during the past 100 years in Kitanada Bay, Southwest Japan were reconstructed, based on the data on grain size, total organic carbon (TOC), total nitrogen (TN) and total sulfur (TS) concentrations, ratio of total organic carbon to total nitrogen (C/N) and to total sulfur (C/S) in surface sediments and sediments cores. The grain size distribution pattern in surface sediment at the present study site showed predominance of coarser sediments around the bay mouth and more finer towards the bay interior, suggesting that tidal current is more swift around the bay mouth and its velocity decreases toward bay interior. The present results indicate a stagnant hydrodynamic condition in inner Kitanada Bay. High levels of TOC, TN and TS concentrations around fish farming cages in the north suggest the use of large quantities of organic substances for fish farming. Benthic environment has become highly reductive due to the supply of organic substances in combination with stagnant hydrodynamic environment. TOC and TN concentrations in sediment cores (33∼79cm) showed an increase from 1970’s when fish farming started. This result suggests that Kitanada Bay has become eutrophic due to fish farming. At the same time, grain size profiles show a decrease in grain size toward the top, while it is reverse in the southern and bay mouth area. This result suggests a transformation in the hydrodynamic environment by the resistance perpetrated on tidal current by fish cages. In the northern area of Kitanada Bay, hydrodynamic environment has become stagnant. In the southern and bay mouth area where no fish cages are observed, tidal current has become more agile. As the result, sea water exchange has become more active, and bottom environment has become less reductive.
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  • Rapid uplifting in the northern part of Hida Mountain Range at 1 Ma, based on lithofacies and petrography in the Iyari Formation.
    Teruki Oikawa, Hajime Wada
    Article type: scientific monograph
    Subject area: Infomation Science
    2004 Volume 110 Issue 9 Pages 528-535
    Published: 2004
    Released on J-STAGE: January 07, 2005
    DOIhttps://doi.org/10.5575/geosoc.110.528
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    The Iyari Formation crops out on the faces of the eastside of the Hida Mountain Range, central Japan. As previously reported, reversed paleomagnetic polarity of this formation is correlated to the Matsuyama Chron. Hence, the estimated depositional age of the Iyari Formation is sometime between 1.65 Ma and 0.78 Ma. The Iyari Formation mainly consists of a gravel bed containing clasts (long axis over 128 mm) of brown or gray welded-tuff (70 %), granitoids (25 %), and green or dark-green welded-tuff (5 %). From the petrographic viewpoints, origin of these clasts is considered to be the Hida Mountain Range. Furthermore, clasts of fine-grained biotite-granite containing mafic microgranular enclave in the Iyari Formation are derived from the Kurobegawa Granite, the northern Hida Mountain Range. Because radiometric ages of the Kurobegawa Granite (1.5-1.0Ma: zircon FT age and biotite K-Ar ages) are almost similar to the estimated depositinal age of the Iyari Formation, it is strongly indicated that the northern Hida Range uplifted and eroded rapidly after ca.1.5-1.0 Ma.
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  • Rock magnetism and paleomagnetism of a lava dome of Tomuro Volcano, Ishikawa Prefecture, Japan
    Hiroyuki Hoshi, Akira Ishiwatari
    Article type: scientific monograph
    Subject area: Infomation Science
    2004 Volume 110 Issue 9 Pages 536-544
    Published: 2004
    Released on J-STAGE: January 07, 2005
    DOIhttps://doi.org/10.5575/geosoc.110.536
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    We have investigated rock magnetic properties and remanent magnetization directions of samples collected from a lava dome of Tomuro Volcano, an andesitic mid-Pleistocene volcano located on the Japan Sea side of central Honshu. Detailed thermal demagnetization experiments and rock magnetic investigations including analyses of isothermal remanent magnetization and anhysteretic remanent magnetization specify the mineralogy, concentration, and grain size of magnetic minerals in andesite samples. Magnetite and hematite are identified as magnetic carriers. However, each mineral concentration differs between bluish andesite (so-called Ao-Tomuroishi) and reddish one (Aka-Tomuroishi); the latter contains more hematite and less magnetite than the former. Magnetic granulometry shows that magnetite in reddish andesite is finer than that in bluish one. At the Mt. Tomuro andesite dome, bluish andesite constitutes the majority of the dome whereas reddish andesite occurs as highly oxidized parts at the dome surface. Based on these observations, we conclude that in reddish andesite, high-temperature oxidation of magnetite grains caused their partial change to hematite and, as a result, reduced their effective grain sizes. Inconsistent site-mean directions were determined at three sites, although they all have northerly directions of normal polarity. This inconsistency would be explained by assuming deformation of lava at the dome surface below blocking temperatures of magnetite and hematite.
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  • Macaronichnus segregatis-like traces found in the modern foreshore sediments of the Kujukurihama Coast, Japan
    Masakazu Nara, Koji Seike
    Article type: scientific monograph
    Subject area: Infomation Science
    2004 Volume 110 Issue 9 Pages 545-551
    Published: 2004
    Released on J-STAGE: January 07, 2005
    DOIhttps://doi.org/10.5575/geosoc.110.545
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    Macaronichnus segregatis-like traces, mostly horizontal to subhorizontal, unbranched, light mineral sand-filled burrows surrounded by heavy mineral halo, are found from modern foreshore sand of Kujukuri-hama Coast, central Japan. Although some workers have considered trace fossil M. segregatis in Quaternary sediments of Japan as locomotion traces of isopod Excirolana chiltoni, the isopod was not collected from the modern sediments in which the traces occur. On the other hand, the trace-bearing sediments contain many individuals of opheliid polychaete which is well known as a trace maker of modern M. segregatis-like traces in the North America. This suggests that the traces found in the foreshore sediments of the Kujukuri-hama Coast are also produced by the opheliids.
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