The Journal of the Geological Society of Japan
Online ISSN : 1349-9963
Print ISSN : 0016-7630
ISSN-L : 0016-7630
Volume 121, Issue 11
Displaying 1-3 of 3 articles from this issue
Articles
  • Relationship between the Oeyama ophiolite and “Maizuru arc”
    Yoshiaki Sugamori, Akira Ishiwatari
    2015 Volume 121 Issue 11 Pages 391-401
    Published: November 15, 2015
    Released on J-STAGE: February 27, 2016
    JOURNAL FREE ACCESS
    The Inagawa Complex, located in Kawanishi City, Hyogo Prefecture, southwestern Japan, is interpreted as a late Permian subduction-related accretionary complex of the Ultra-Tamba Terrane. The complex contains a conglomerate bed, with clasts consisting predominantly of felsic volcanic rocks, serpentinite, and schist, with subordinate amounts of granite, basalt, and sedimentary rock (chert and mudstone, containing late Paleozoic radiolarians). The provenance of the conglomerate is inferred to be a volcanic arc, where volcanic rocks overlay an accretionary complex, sedimentary rocks, metamorphic rocks, and granite. Serpentine grains contain spinel crystals that are unaltered in their cores and exhibit highly irregular shapes resembling so-called “dancing spinel”, which are characteristic of mantle peridotites of the early Paleozoic Oeyama ophiolite. Geochemical analysis of the spinel crystals (Cr#50-51 and Cr#42) confirms that they originate from the Oeyama ophiolite. The discovery of serpentinite from the Oeyama ophiolite in the late Permian subduction-related accretionary complex of the Ultra-Tamba Terrane suggests that the Oeyama ophiolite was exposed in the forearc area of the Permian “Maizuru (Yakuno) arc”, which was floored predominantly by oceanic crust of the Permian Yakuno ophiolite.
    Download PDF (3440K)
  • Michiharu Ikeda, Tomohiro Tsuji, Hideaki Goto, Hiroyuki Tsutsumi, Masa ...
    2015 Volume 121 Issue 11 Pages 403-419
    Published: November 15, 2015
    Released on J-STAGE: February 27, 2016
    JOURNAL FREE ACCESS
    Supplementary material
    Four cores (Br. A-D, from north to south) were taken across the estimated trace of the Kawakami Fault at Yokoguro, Saijo City, in order to obtain geological evidence regarding the nature of the geomorphologically defined fault trace. The Kawakami Fault is part of the Median Tectonic Line Active Fault Zone, which is a 400-km-long right-lateral strike-slip fault. The Kawakami Fault is ~30 km long and strikes N70°E. Sedimentary textures in the cores were analyzed in terms of sedimentary structure, color, volcanic ash content, magnetic susceptibility, and micro fossil content. Four units (Units 1-4) are recognized in Br. A, B, and C, whereas Unit 4 is not encountered in Br. D, which was obtained from the downthrown side of the fault. The K-Ah horizon (7300 yrs BP) in Br. C is ~2.24 m shallower than in Br. D. The boundary between Unit 3 and Unit 4, which is located below the K-Ah horizon, occurs > 6.0 m higher in Br. C than in Br. D.The differences in depth between corresponding layers in Br. C and Br. D increase progressively with depth. In addition, each unit in Br. C is thinner than in Br. D. These observations, combined with groundwater level information, indicate that the Kawakami Fault is located between Br. C and Br. D, and that the fault has moved repeatedly with a down-to-the-south sense of displacement. Depth differences between corresponding layers in Br. B and Br. C show a similar trend to the differences between Br. C and Br. D, suggesting that a flexure structure exists between Br. B and Br. D. Using the calculated fault displacements (~2.24 m between Br. C and Br. D, and ~4.03 m between Br. B and Br. D) that have occurred since ~7300 yrs BP (as calculated using the K-Ah horizon), the vertical slip-rate of the Kawakami Fault at Yokoguru is ~0.3 mm/yr, or ~0.55 mm/yr in the case that a flexure structure exists between Br. B and Br. D.
    Download PDF (8618K)
Note
  • Examples of quartz and calcite
    Takuto Kanai, Kojiro Moriyama, Hideki Mukoyoshi, Hideo Takagi
    2015 Volume 121 Issue 11 Pages 421-427
    Published: November 15, 2015
    Released on J-STAGE: February 27, 2016
    JOURNAL FREE ACCESS
    Crystallographic orientations of minerals were determined by electron backscatter diffraction (EBSD) under a scanning electron microscope. In this study, we introduce a technique for vibratory polishing of rock samples using colloidal silica (CS), for EBSD analysis of quartz in granite and calcite in limestone. Evaluation of the surface state consisted of a band contrast (BC) measure to represent the surface state, a hit rate to represent the success rate of indexing, and a mean angular deviation (MAD) to represent the accuracy of indexing. The factor that most affected the BC and the hit rate was the total amount of displacement of the sample. However, the BC and hit rate also showed a dependency on the crystallographic orientation. When eight Kikuchi bands were detected, the value of the MAD was < 1°, and the MAD was independent of the BC. The BC measure showed that the optimal CS polishing times for quartz and calcite were 3 hours and 1 hour, respectively. When preparing a sample with for the first time, CS polishing for 3 hours and detection of the eight Kikuchi bands provide the most effective method for determining crystallographic orientations.
    Download PDF (2223K)
feedback
Top