BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN
Online ISSN : 2186-490X
Print ISSN : 1346-4272
ISSN-L : 1346-4272
Volume 70 , Issue 5
Showing 1-2 articles out of 2 articles from the selected issue
research-article
  • Toru Yamasaki
    Type: research-article
    2019 Volume 70 Issue 5 Pages 335-355
    Published: November 25, 2019
    Released: November 27, 2019
    JOURNALS FREE ACCESS

    During the national mapping project for Quadrangle Series, 1:50,000, Akechi District, a granitic mass with 4 × 3.5 km in diameter at the Akechi Higashigata area, Ena City, Gifu Prefecture, central Japan was newly confirmed. The granitic mass is separated into Eastern and Western masses by overlying Akechi Conglomerate. Based on the results of whole-rock geochemical analyses, the Earstern Mass and Western Mass are correlate with the Busetsu Granite and Naegi-type biotite granite, respectively. The Busetsu Granite is characterized by relatively clear whole-rock geochemical trends and chondrite-normalized rare earth element patterns showing gentle slopes up to the left with negative Eu anomaly. On the other hand, the biotite granite shows rather scatterd whole-rock geochemistry and relatively flat rare earth element patterns with clear negative Eu anomaly. Most of the samples from the Busetsu Granite show higher alumina saturation index (>1.1) and fractionation of garnet from sediment-origin parental melt is suggested. On the contrary, the biotite granite show wide range of alumina saturation index due to heterogeneous assimilation of host pelitic metamorphic rocks. Although the parental magma of the Naegi-type granite (including biotite granite in the study area) has probably been similar to that of the metaluminous granites in the Ryoke Belt in the Chubu district, partial melting at shallower crustal condition has possibly resulted in SiO2-rich nature of the Naegi-type granite.

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  • Takayuki Uchino
    Type: research-article
    2019 Volume 70 Issue 5 Pages 357-372
    Published: November 25, 2019
    Released: November 27, 2019
    JOURNALS FREE ACCESS

    U–Pb ages of detrital zircon from sandstone samples from the Jurassic accretionary complex in the southwestern margin of the North Kitakami Belt in the Sotoyama District, Iwate Prefecture, were examined in this study. Four samples were collected at four locations from the boundary area between the North Kitakami and Nedamo belts to the northeastward: the Tatezawa, Yonaigawa, Okawa and Mukaizawa samples, respectively.

    Zircon from the Tatezawa and Yonaigawa samples shows youngest cluster ages of c.a. 190 Ma, and these sandstone samples probably deposit in the Early Jurassic. Zircon from the Okawa Sample shows a youngest cluster age of c.a. 260 Ma, and this sandstone sample probably deposit in the Late Permian, Late Triassic or Early Jurassic. Zircon from the Mukaizawa Sample shows a youngest cluster age of c.a. 170 Ma, and this sandstone sample probably deposit in the Middle Jurassic.

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