The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 105, Issue 3
Displaying 1-9 of 9 articles from this issue
  • Toshihiko Sakashima, Toru Takeshita, Tetsumaru Itaya, Yasutaka Hayasak ...
    1999 Volume 105 Issue 3 Pages 161-180
    Published: March 15, 1999
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    The Ryuhozan metamorphic sequence in the southern Higo belt, Japan is lithologically divided into two formations ; the lower formation (total thickness, ca. 950 m) consisting of limestone and chloritoid rocks intercalated by metamorphosed basic-acidic volcanic and volcanoclastic rocks, and pelites and psammites, and the upper formation (total thickness, ca. 850 m) consisting of slates, and bedded and massive limestone. The geologic structure is characterized by an E-W trending and vertically dipping schistosity which was truncated by sinistral trunscurrent faults of NE-SW strike. The sinistral sense of shear can be inferred from more than 70% of the asymmetric microstructures (n=48) such as shear band, shape and lattice fabric of quartz and calcite (i.e. shear sense indicators). Considering also the development of isoclinal folds with E-W trending axis, a large amount of shortening in NS direction and E-W trending left-lateral shear seem to have concurrently occurred in the zone (a left-lateral transpression).Both type I and type II crossed girdle c-axis fabric patterns are developed in the elongated quartz aggregates parallel to the schistosity. The fact suggests that the deformation occurred at the temperature conditions equivalent to the greenschist to amphibolite facies, being consistent with the mineral assemblages (up to hornblende+andesine) observed in the closely associated basic rocks. Hornblende, muscovite and biotite forming schistosity give ca. 100 Ma in K-Ar age, suggesting that the Ryuhozan metamorphic rocks were formed in a Cretaceous regional tectonometamorphic event which affected the whole Higo metamorphic belt.The host lithologies for the Ryuhozan metamorphic rocks were a sedimentary sequence dominant in volcanic and volcanoclastic rocks with bimodal compositions intercalated by impure limestones and laterites, which suggests the depositional setting either at a volcanic arc or at a passive margin which occurred temporarily from Carboniferous to Permian in the Asian continent. This Ryuhozan metamorphic sequence is correlative with the South Kitakami belt and the Hitachi metamorphic sequence based on their protolithic and tectonometamorphic similarities.
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  • Masaki Yuhara, Hiroo Kagami
    1999 Volume 105 Issue 3 Pages 181-192
    Published: March 15, 1999
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Geological, petrological and chronological studies of the Takato granite, which is exposed in the Ina district of the Ryoke belt, have been carried out. The Takato granite intruded into the Ryoke metamorphic rocks which are composed of mainly pelitic and psamitic metamorphic rocks and consits of two bodies (northern and southern bodies) in the field. The northern body mainly consists of medium grain biotite granodiorite, and biotite granite and hornblende - biotite tonalite. The southern body is composed of hornblende-biotite tonalite. Based on mineral assemblage and whole rock chemical composition, biotite granodiorite and biotite granite, which are main constituent rock types of the northern body, were formed from dissimilar magma to the southern body and southern part of the northern body. Thus, we call biotite granodiorite to granite and hornblende - biotite tonalite "Takato granodiorite" and "Takato tonalite", respectively. The Takatao granodiorite gives a Rb-Sr whole rock isochron age of 85.2±6.6 Ma with an initial Sr isotopic ratio of 0.70774±0.00017. This age indicates time of activity of the Takatao granodiorite.Activity of the Takato tonalite is older than the Takato granodiorite. An initial Sr and Nd isotopic ratios of the Takato granodiorite are in range of initial isotopic ratios of the Ryoke granite.
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  • Shiro Tanaka, Mamoru Adachi
    1999 Volume 105 Issue 3 Pages 193-199
    Published: March 15, 1999
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Garnets, rich in Mg as high as MgO=10.4 wt.% (39.5 pyrope mol%), have been found in a fine-grained rutile-graphite-garnet-biotite-quartz gneiss clast (Sawa-13) and a coarse-grained microcline-garnet-biotite-quartz-oligoclase gneiss clast (Sawa-43) from the Jurassic Sawando conglomerate in the northeastern part of the Mino terrane.This discovery gives a definite picture for the source rock of detrital Mg-rich garnets that are common in the Jurassic sandstones of the Mino terrane. Judging from the textures and chemical compositions of minerals of gneiss clasts, Sawa-13 and Sawa-43 are likely to have been metamorphosed under the granulite facies conditions and subsequently metamorphosed retrogressively.
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  • Katsuyoshi Michibayashi, /, [in Japanese]
    1999 Volume 105 Issue 3 Pages 200-207
    Published: March 15, 1999
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Mylonite drill core has been obtained from 150 m to 300 m below the surface in the Ryoke metamorphic belt only 100 m away from the Median Tectonic Line. The drill core consists of the Ryoke metasedimentary rocks, such as metapelite and metachert, and mylonitized igneous rocks. The latter rocks do not occur at the surface in this vicinity but are the same as porphyroclastic mylonite outcropping to the north. The major lithological boundary between the metasedimentary rocks and the granitic rocks occurs at approximately 265 m below the surface, which is consistent with that predicted previously by a Yamamoto and Masuda's 3-D structure model. Preliminary microstructural analyses revealed that although the whole of the core is mylonitized, strain is localized to a zone of about 10 m width across the major lithological boundary.
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  • Katsumi Kimura
    1999 Volume 105 Issue 3 Pages 208-226
    Published: March 15, 1999
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    Detailed kinematic analysis of thrust faults in a coherent accretionary complex, called the Inuyama Sequence, in the Mino-Tamba Belt, central Japan, have been carried out in a 3 km-long route along the Kiso River. The Inuyama Sequence in the study area is characterized by stacking of six regional-scale thrust sheets deformed by later-stage of W-plunging synform structure. Each sheet consists of an Early Triassic to Middle Jurassic oceanic plate stratigraphic succession. Slip-directions of thrust faults were, after correction of folding and tilting, calculated with pitches of slickenlines for 19 faults, a fabric of a duplex for one fault, and the slip-sense determined with mesoscopic and microscopic asymmetric structures. Left-lateral strike-slip faults also occur in the Inuyama Sequence, but they can be distinguished from thrusts based on differences of pitches of slickenlines and associated deformation features. The mean slip-direction of thrust faults are oriented to S30°E with respect to the N60°E-S60°W regional trend of the Inuyama Sequence. After restoration of rotation and bending of Southwest Japan, the mean slip-direction is probablly parallel to the normal subduction of the Izanagi Plate under the Asia Plate during the latest Jurassic to earliest Cretaceous.
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  • Jun-ichi Tazawa
    1999 Volume 105 Issue 3 Pages 227-230
    Published: March 15, 1999
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    The following three species of the typical Boreal-type brachiopod genus Yakovlevia occur from the Middle Permian of the Hida Gaien and South Kitakami Belts, Japan : Y. kaluzinensis Fredericks, Y. mammata (Keyserling) and Y. mammatiformis (Fredericks). The occurrence of Yakovlevia together with various many Boreal-and Tethyan-type brachiopods in the Middle Permian of the Hida Gaien and South Kitakami Belts provides evidence that these regions were a continental shelf at the eastern margin of the Sino-Korean block in the Middle Permian time.
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  • Aiming Lin, Takuya Wada, Tadashi Maruyama
    1999 Volume 105 Issue 3 Pages 231-234
    Published: March 15, 1999
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    The Ashiya fault, one of the main faults of the Rokko-Awaji fault zone, central Japan, has been considered as an inactive fault during the late Quaternary (Nakata et al., 1996 ; Suzuki et al., 1996). An outcrop of the Ashiya fault showing the activity during recent 30, 000 y, however, was found at a construction site, on the northern side of Sakasegawa-river, Takarazuka City. The deposits at this outcrop consist of unconsolidated sand and gravel beds with thin layers of silt and clay, which were offset at least 5 m in vertical.The radiocarbon dating and pollen analysis show that the deposits had been formed since 33, 780 y.B.P. which can be compared with that of Tenma formation distributed in the area around the Osaka basin. Detailed observations and sketches show that there are at least five seismic faulting events since about 30, 000 y.B.P.
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  • Kiyohide Mizuno, Eikichi Tsukuda, Makoto Takahashi, Arata Momohara, Ta ...
    1999 Volume 105 Issue 3 Pages 235-238
    Published: March 15, 1999
    Released on J-STAGE: April 11, 2008
    JOURNAL FREE ACCESS
    An all-core boring reaching 625 m in depth was conducted at Negoro in the Wakayama Plain which is a tectonic basin formed under the influence of the Median Tectonic Line active fault system. At the depth of 137m, sedimentary rocks belonging to the Upper Cretaceous Izumi Group and their sheared materials (lithologic unit : NG-1) are in contact with unconsolidated sediments by a reverse fault dipping about 30° northward. Unconsolidated sediments are composed of a sequence of alternating beds of pebble, sand and silt intercalating peaty layers and a volcanic ash layer (V290). They are divided lithologically into 4 units (NG-2 to NG-5). Some plant macrofossils were collected and paleomagnetic measurements were carried out. The sequence is divided into Zone 1, Zone 2 and Zone 3 in descending order on the basis of paleomagnetic polarities, and Zones 1, 2 and 3 are correlative to the Matuyama, Gauss and Gilbert chrons respectively, as the result of the correlation of widespread tephras and biostratigraphic constraints of plant fossils. These unconsolidated sediments correspond to the beds of the Shobudani Formation distributed in the hills, east of the Wakayama Plain. It is presumed that the formation has gently tilted northward in the basin and has contacted with the basement rocks by a fault at the northernmost part of the plain.
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  • Toshihiko Sugai, Yasuo Awata, Ryo Anma, Yukiyasu Saka
    1999 Volume 105 Issue 3 Pages V-VI
    Published: 1999
    Released on J-STAGE: November 26, 2010
    JOURNAL FREE ACCESS
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