Journal of Mineralogical and Petrological Sciences
Online ISSN : 1349-3825
Print ISSN : 1345-6296
ISSN-L : 1345-6296
Advance online publication
Displaying 1-3 of 3 articles from this issue
  • Yasuyuki BANNO
    Article ID: 231218b
    Published: 2024
    Advance online publication: March 07, 2024
    JOURNAL FREE ACCESS ADVANCE PUBLICATION

    Wollastonite of variable cathodoluminescence (CL) intensity was found in a skarn xenolith from Tadano, Fukushima Prefecture, Japan. Electron microprobe analysis revealed bright-blue and faint-blue CL spots in crystals. Panchromatic CL images revealed that individual wollastonite grains often include bright and dark CL regions of bright- and faint-blue CL, respectively. The TiO2 contents of bright CL regions (0.055–0.110 wt%) were higher than those of dark CL regions (<0.008–0.013 wt%). The blue CL intensity gradually increased from <0.008 to 0.102 wt% TiO2, and that with 0.102 and 0.110 wt% TiO2 was almost the same. The results indicated a positive correlation of Ti content with blue CL intensity.

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  • Sara AL-BUSAIDI, Atsushi KAMEI, Sasidharan A. SILPA
    Article ID: 230908
    Published: 2024
    Advance online publication: February 20, 2024
    JOURNAL FREE ACCESS ADVANCE PUBLICATION

    Shimane Peninsula in the San’in region, SW Japan, has preserved a wide distribution of igneous rocks related to back-arc rifting in the Miocene. We investigated the petrography, geochemistry, and Sr-Nd isotope systematics of rhyolite lavas (Josoji rhyolite: 18-15 Ma) and basaltic to andesitic intrusions of Stage I (ca 14 Ma) and II (ca 13 Ma) intrusive rocks. They are classified as medium-K magma series. The Josoji rhyolite and Stage I rocks show chemical compositions of arc-type signatures, whereas the Stage II rocks show elevated Nb and Ta abundances suggesting weaker arc signatures. The geochemical characteristics indicate that the Josoji rhyolite was produced by partial melting of arc-type basalt under lower to middle crustal conditions. The arc signatures of the Stage I rocks were inherited from a remnant metasomatized lithosphere formed by the subduction of the Pacific Plate before the opening of the Japan Sea. The Stage II rocks were formed from a fertile magma that might be produced by the melting of upwelling asthenospheric mantle. We conclude that various magmatic processes took place during and just after the back-arc rifting development in the San’in region.

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  • Satoshi Nakano
    Article ID: 230630
    Published: 2024
    Advance online publication: January 30, 2024
    JOURNAL FREE ACCESS ADVANCE PUBLICATION

    Feldspar internal textures in a pyroclastic trachyte from Oki-Dogo, Sea of Japan, were examined to expand the understanding of feldspar reactions during the cooling through magmatic to hydrothermal stages, beyond the previous information of feldspars in Oki-Dogo alkaline lava and sheet rocks, using the methods of an electron microprobe and cathodoluminescence. Two types of micron-size internal microtextures were found to coexist in individual feldspar phenocrysts: clear domain textures, formed during a high-temperature magmatic stage, and turbid microperthitic textures, formed during a low-temperature subsolidus stage. The both microtextures are products of metasomatic replacement reactions. In addition, nano-size fluorite grains are aligned across the microtextures. The fluorite occurrence records the behavior of fluorine related to feldspar reactions. The first account of metasomatic microtextures crosscut by fluorite alignments in volcanic alkali feldspars expands our knowledge of feldspar reactions during the cooling and fluorine behaviors related to them in igneous rocks, and shows the significance of the careful analysis of feldspar internal microtextures.

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