Journal of Mineralogical and Petrological Sciences
Online ISSN : 1349-3825
Print ISSN : 1345-6296
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Volume 111 , Issue 6
December
Showing 1-9 articles out of 9 articles from the selected issue
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Editorial
ORIGINAL ARTICLES
  • D. Nuwan Sanjaya WANNIARACHCHI, Masahide AKASAKA, Yasutaka HAYASAKA, L ...
    Volume 111 (2016) Issue 6 Pages 373-384
    Released: January 12, 2017
    JOURNALS FREE ACCESS

    Internal textures and U–Pb ages of zircons in garnet–biotite gneiss of the Southwestern Highland Complex (SWHC), Sri Lanka, were studied to clarify the repeated thermal events in the study area. The zircons from garnet–biotite gneiss consist of the detrital cores and overgrowths with two to five growth stages. The detrital zircon cores are rounded or euhedral to subhedral in shape, and show transgressive internal textures or oscillatory zoning.

     The rounded or subhedral to euhedral detrital core morphology suggests several major Archaean to Proterozoic sources of detritus zircons in the SWHC. Ages of the detrital cores are in a range of 3.3–1.7 Ga, and can be categorized into five ranges of 3380–3220, 2730–2660, 2550–2490, 2220–2170, and 1900–1700 Ma, implying the source rock ages. The detrital cores in the 3380–2170 Ma have Th/U–ratios of more than 0.3, suggesting igneous origin. The detrital cores in the range 1900–1700 Ma have Th/U of >0.3 or 0.3–0.1, suggesting an igneous or metamorphic origin. Some overgrowths with the ages in the ranges of 1900–1700 and 630–500 Ma have Th/U–ratios less than 0.1 implying that zircon growth corresponds to the thermal events. Zircons lacking detrital cores and having growth zones with characteristic metamorphic internal textures gave ages in a range of 630–500 Ma, implying the generation at the final granulite grade metamorphic event.

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  • Yurie NAKAMURA, Takahiro KURIBAYASHI, Toshiro NAGASE
    Volume 111 (2016) Issue 6 Pages 385-397
    Released: January 12, 2017
    JOURNALS FREE ACCESS

    The cation ordering of the {110}c and {211}c growth sectors in birefringent garnet from Kayas, Mali was investigated by means of single–crystal X–ray diffraction (SC–XRD) method The chemical compositions of the {110}c and {211}c sectors were determined as (Ca2.96Mg0.04Mn0.04)Σ3.04(Fe0.97Al0.95Ti0.11)Σ2.03Si2.93O12, and (Ca2.91Mg0.05Mn0.03)Σ2.99(Fe1.01Al0.90Ti0.14)Σ2.05Si2.93O12, respectively. Reflections that violate the extinction rule for the space group Ia3d were observed, and crystal structure models for both the {110}c and {211}c sectors should have triclinic symmetry with the space group I1. The unit–cell parameters of both growth sectors were a = 11.9739(13), b = 11.9742(14), c = 11.9737(13) Å, α = 90.001(9), β = 90.098(9) and γ = 90.014 (10)° for the {110}c sector; a = 11.952(6), b = 11.952(6), c = 11.957(6) Å, α = 90.06(4), β = 90.01(4) and γ = 89.94(4)° for the {211}c sector. Structure refinements for I1 models of both sectors were convergent with R1 = 3.02 and 3.36%, respectively. There were significant differences in the Fe3+ distribution trend in the Y sites between the {110}c and {211}c sectors. The Fe3+ occupancies of the eight Y sites in the {110}c sector were 66.9(8), 66.0(8), 63.2(8), 60.0(8), 49.8(8), 49.5(8), 47.8(8), and 46.7(8)%. The octahedral Y sites of {110}c sector can be divided into two groups. In terms of symmetry, Fe3+ distribution in the Y site of the {110}c sector appeared to be pseudo–orthorhombic. In contrast, the Fe3+ distributions in the eight Y sites of the {211}c sector as follows: 60.0(10), 41.9(10), 62.7(10), 69.1(10), 55.5(10), 53.2(10), 55.7(10), and 43.5(10)%. The Fe3+ occupancies in the Y sites of the {211}c sector were random and different from that of the {110}c sector. Different cation distributions between the growth sectors in the Mali garnet indicate that cation ordering in the crystal structure was formed during growth. These observations suggest that the differences in the Fe3+ distribution between the {110}c and {211}c sectors are strongly affected by the growth process in each sector.

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  • Kenta YOSHIDA, Naoki AOYAGI, Ryoji KATO, Takao HIRAJIMA
    Volume 111 (2016) Issue 6 Pages 398-404
    Released: January 12, 2017
    JOURNALS FREE ACCESS

    Thermal structure of the Kebara Formation and its proximal areas in the western Kii Peninsula was examined by Raman spectra of carbonaceous material (RSCM) geothermometer for pelitic rocks. A mean temperature of 313 ± 5 °C is obtained for the Kebara Formation, which is comparable with that of the neighboring unit of the Mikabu belt (319 ± 5 °C). The Sanbagawa belt of the relevant area, within a few kilometers to the north of the Kebara Formation, shows a mean temperature of 285 ± 7 °C, which is slightly but evidently lower value than those of the above two units. Peak temperatures estimated from the Chichibu belt and Shimanto belt located to the south of the Kebara Formation are 289 ± 13 °C and 216 ± 24 °C, respectively. Published geochronological data of the Kebara Formation are slightly older than those of the Sanbagawa belt in the Kii Peninsula and are similar to those of the Mikabu belt in the relevant area. These two data sets (geothermometry and geochronology) suggest that the Kebara Formation is possibly correlated with the Mikabu belt, but is not coherent to the southern margin of the Sanbagawa belt in the western Kii Peninsula, in tectonic contact with each other.

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  • Takahiro MIYAZAKI, Daisuke NAKAMURA, Akihiro TAMURA, Martin SVOJTKA, S ...
    Volume 111 (2016) Issue 6 Pages 405-419
    Released: January 12, 2017
    JOURNALS FREE ACCESS

    Eclogites from the Moldanubian Zone of the Bohemian Massif (Czech Republic) have experienced ultrahigh–pressure (UHP) and ultrahigh–temperature (UHT) metamorphic conditions (P > 4.0 GPa, T > 1000 °C). One eclogite sample collected from Nové Dvory, eastern part of Czech Republic, contains leucocratic pockets. The mineral assemblage of the melanocratic part of the eclogite is garnet + omphacite + rutile + later–stage minerals (biotite + amphibole + plagioclase). The leucocratic pockets mainly consist of plagioclase and include moderate amounts of garnet and clinopyroxene + small amounts of biotite and amphibole. Garnet and clinopyroxene grains in the leucocratic pockets display faceted shapes whereas those in the melanocratic part show irregular shapes. These are consistent with the idea that garnet and clinopyroxene grains in the leucocratic pockets had been surrounded by melt, as melt can provide free space for the formation of such faceted shapes. The major and trace element composition of garnet grains in the melanocratic part are the same as those in the leucocratic pockets. Clinopyroxene also shows the same major and trace element composition for irregular shape grains in the melanocratic part as faceted grains in the leucocratic pockets. If the melt had originated from the gneiss surrounding the peridotite body with eclogite lenses or layers, the composition of clinopyroxene in the leucocratic pockets would have been completely different from that in the melanocratic part. In addition, the trace element composition of melt estimated from clinopyroxene composition resembles that of Tonalite – Trondjhemite – Granodiorite (TTG), which can be produced by partial melting of eclogite. Thus, these observational and analytical data suggest that the leucocratic pockets were originally melt that was internally produced by partial melting of the eclogite.

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LETTERS
  • Akio SUZUKI
    Volume 111 (2016) Issue 6 Pages 420-424
    Released: January 12, 2017
    JOURNALS FREE ACCESS

    A new synchrotron X–ray diffraction study of ε–FeOOH has been carried out to determine the pressure–volume–temperature (PVT) equation of state (EOS). The PVT data fitted a third–order Birch–Murnaghan EOS yielded: isothermal bulk modulus KT0 of 135(3) GPa; its pressure derivative K′ of 6.1(9); (∂KT/∂T)P of −0.05(2) GPa K−1; a0 of 2.6(7) × 10−5 K−1 and a1 of 1.0(3) × 10−7 K−2, where the volumetric thermal expansion coefficient is described as α0,T = a0 + a1 × (T − 300).

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  • Masami KANZAKI
    Volume 111 (2016) Issue 6 Pages 425-430
    Released: January 12, 2017
    JOURNALS FREE ACCESS

    In synthetic hydroxyl–chondrodite and hydroxyl–clinohumite, two hydrogen sites (H1 and H2) are known. However, hydrogen occupying only H1 site has been reported for natural F– and Ti–rich chondrodite and clinohumite. In order to understand hydrogen distribution in these sites, stability of hydrogens at these sites in chondrodite is studied by first–principles density functional theory calculation. For hydroxyl–chondrodite, lowest energy was found when both H1 and H2 sites are half occupied by hydrogens. In this configuration, strong H1–H1 repulsion is avoided, and nearly straight hydrogen bond of O–H1•••O–H2 is realized. When a half of OH is replaced with F or replaced with O2− in the case of Ti–containing systems, hydrogen occupying H1 site is always favored over hydrogen in H2 site so as to form nearly straight hydrogen bond of O–H1•••F (or O2−). Our calculations are fully consistent with the observed structures in both synthetic and natural chondrodite, and revealed that hydrogen distribution in humite group minerals is mostly governed by hydrogen bonding at H1 site.

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