Online ISSN : 2186-490X
Print ISSN : 1346-4272
ISSN-L : 1346-4272
Volume 67 , Issue 2
Showing 1-2 articles out of 2 articles from the selected issue
  • Shunso Ishihara, Tetsuji Ohno
    2016 Volume 67 Issue 2 Pages 41-58
    Published: June 20, 2016
    Released: September 01, 2016
    Geochemical and geomagnetic character of the Late Cretaceous-Paleogene granitic batholith was examined at N-S transect across the city of Hiroshima. The granitoids are mostly biotite granite in composition, but granodiorite predominates in the Takanawa Peninsula. Their magnetic susceptibility is the highest in the Sanin belt, but becomes lower of the ilmenite-series to the south and lowest in the southernmost Ryoke belt. The granitoids are most sodic in the Sanin belt and potassic in the Sanyo and Ryoke belts, which may reflect igneous and sedimentary source rocks, respectively. The alumina saturation index (A/CNK) is above 1.0, i.e., peraluminous, but never exceeding 1.1 for S-type granite. Rb and Pb replacing K are the least in the Sanin belt but the highest in the Ryoke and southern Sanyo belts. High-Sr granitoids and adakite of the northern Kyushu and the Kinki district were not found in the studied regions. Zircon saturation temperatures in the average of the studied granitoids are the highest of 753oC in the Ryoke belt, because granodiorite predominates here.
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  • Daisuke Araoka, Yoshiaki Kon, Terumi Ejima
    2016 Volume 67 Issue 2 Pages 59-65
    Published: June 20, 2016
    Released: September 01, 2016
    U-Pb zircon dating is a useful method for determining precise ages of solidification of igneous rocks within a wide range of geological time scale. Thus, we set up SHRIMP (Sensitive High Resolution Ion MicroProbe) U-Pb zircon dating method and sample preparation procedure for SHRIMP analysis in a laboratory of Geological Survey of Japan, AIST. First, zircons in the samples were separated effectively using SHLFRAG Lab (high voltage pulse power fragmentation), heavy liquid, and so on. The separated zircons were mounted on resin followed by polishing, Au-coating, and cathodoluminescence observation. Then, SHRIMP U-Pb ages of zircon reference materials (R33, OG1, and 91500) with Paleozoic to Eoarchean Era were determined. All dating results were corresponding to the reference ages within the analytical error, indicating that accurate SHRIMP U-Pb zircon dating could be established in AIST.
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