Journal of Mineralogical and Petrological Sciences
Online ISSN : 1349-3825
Print ISSN : 1345-6296
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Volume 108 , Issue 3
June
Showing 1-8 articles out of 8 articles from the selected issue
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ORIGINAL ARTICLES
  • Masahide AKASAKA, Takehiko KIMURA, Mariko NAGASHIMA
    Volume 108 (2013) Issue 3 Pages 121-130
    Released: July 04, 2013
    [Advance publication] Released: March 26, 2013
    JOURNALS FREE ACCESS
    Babingtonite from Kouragahana, Shimane Peninsula, Japan, was investigated using electron microprobe, X-ray Rietveld, and 57Fe Mössbauer spectral analyses to characterize its chemical compositions, crystal structure, oxidation state of Fe, and distribution of Fe between two crystallographically independent octahedral Fe1 and Fe2 sites.
    The Kouragahana babingtonite occurs as single parallelohedrons with {100}, {001}, {001}, {111}, {110}, and {101} and sometimes shows penetration twinning. Both normal and sector-zoned crystals occur. Babingtonite crystals with sector zoning consist of sectors relatively enriched in Fe and of sectors enriched in Mg, Mn, and Al. Babingtonite also shows compositional zoning with higher Fe2+ and Al core and higher Fe3+ and Mn rim. The average Fe content of the babingtonite without sector zoning is similar to the Fe2+-rich sector of the sector-zoned babingtonite. The chemical formula based on the average composition of all analytical data (n = 193) is [Na0.01(2)Ca2.01(2)] [Mg0.11(4)Mn0.09(3)Fe2+0.76(7)Fe3+0.93(5)Ti0.01(1)Al0.06(5)]Si5.01(4)O14(OH). X-ray Rietveld refinement was carried out using a model of space group P1. The result of the refinement is characterized by R-weighted pattern = 9.91, R-expected pattern = 6.37, and goodness-of-fit = 1.56. The unit cell parameters are a = 7.4667(3), b = 11.6253 (6), c = 6.6820(2) Å, α = 91.533(4), β = 93.886(3), γ = 104.203(4)°, and V = 560.43(4) Å3.
    The refined site occupancies of atoms in the Fe1 and Fe2 sites are [Fe0.91(2)Mg0.09] and [Fe0.91(2)Al0.09], respectively, if Mg is assumed to distribute in the Fe1 site and Al in the Fe2 site. By allocating Mn, 0.09 atoms per formula unit (a.p.f.u.), to the Fe1 site, the site populations in the Fe1 and Fe2 sites are determined as [Fe0.82(2)Mn0.09Mg0.09] and [Fe0.91(2)Al0.09] a.p.f.u., respectively. The 57Fe Mössbauer spectrum taken at room temperature consists of three peaks, which were resolved into two doublets assigned to Fe2+ and Fe3+ at the two octahedral sites. The Fe2+:Fe3+ ratio was determined as Fe2+:Fe3+ = 43.3(3):56.7(4) and 47.1(4):52.9(3) by applying two fitting models, and the average Fe2+:Fe3+ ratio was 45.2(4):54.8(4). The results of X-ray Rietveld analysis and Mössbauer spectroscopy indicate that Fe2+ and Fe3+ are ordered at the Fe1 and Fe2 sites, respectively, in the Kouragahana babingtonite.
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  • Yoshihiro NAKAMURA, Junji AKAI
    Volume 108 (2013) Issue 3 Pages 131-143
    Released: July 04, 2013
    [Advance publication] Released: March 26, 2013
    JOURNALS FREE ACCESS
    Graphitization of carbonaceous material (CM) in the Gyoja-yama contact aureole, northwest of Kyoto, Japan, was examined using high-resolution transmission electron microscopy (HRTEM), X-Ray Diffractometry (XRD), and Micro-Raman spectroscopy. In this region, the CM in the sedimentary rocks has been transformed from poorly crystalline to well-crystallized graphite. This conversion is evident from its morphological transformation of the grain structure to filament like structure and finally into hexagonal plate structure. These microstructural evolutions closely resemble the graphitization process that is usually observed in regional metamorphism, as reported in previous HRTEM observations. Micro-Raman and XRD results indicate that the graphitization parameters are also comparable to each other, where Lc(002) and La(110) values increase during graphitization in contact metamorphism. However, the d002 values have lower correlation coefficients with R2 compared to other parameters. In addition, the crystal size of fully ordered graphite with a d-spacing of ≤3.36 Å in contact metamorphic rocks is approximately 100 Å larger than that in regional metamorphic rocks. These features indicate that information of d002 parameter includes not only the peak metamorphic temperature condition, but also several other factors such as deformation, confining pressure, impurities of fluid activities and catalytic effect, which may be the key point to fully understand the evolution of CM to graphite.
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  • Francesco VETERE, Hiroaki SATO, Hidemi ISHIBASHI, Rosanna DE ROSA, Pao ...
    Volume 108 (2013) Issue 3 Pages 144-160
    Released: July 04, 2013
    [Advance publication] Released: March 26, 2013
    JOURNALS FREE ACCESS
    Viscosity changes during the crystallization of a shoshonitic lava from the Vulcanello peninsula (Aeolian Islands, southern Tyrrhenian Sea, Italy) were measured by use of a electromagnetic rotational viscometer under Ni-NiO buffered conditions at temperatures ranging from 1539 K to 1381 K. Results showed an increase in effective viscosity from 131 Pa s to 15320 Pa s as the crystal content increased from 0 vol% to ∼ 14 vol%. The crystallization processes in the nominally dry shoshonite began at 1420 K with the formation of clinopyroxene, which was followed by the formation of plagioclase and olivine at 1401 K. Experimental observations differed from predictions derived from the use of the Einstein-Roscoe equation with the Marsh (E-R-M) parameter at crystal contents higher than 8 vol%. The relative viscosity of samples was larger than that calculated by E-R-M by a factor of up to 9.5 as the temperature decreased to 1381 K. The large departure of the experimental results from the E-R-M equation predictions was likely caused by the interaction of elongated pyroxene crystals. The measured viscosity data were used to estimate the potential for emplacement of shoshonitic lavas.
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  • Yasuhiro TAKAI, Seiichiro UEHARA
    Volume 108 (2013) Issue 3 Pages 161-165
    Released: July 04, 2013
    [Advance publication] Released: May 02, 2013
    JOURNALS FREE ACCESS
    Hizenite-(Y), ideal formula Ca2Y6(CO3)11·14H2O, occurs in druse of alkali olivine basalt at Mitsukoshi, Karatsu, Saga Prefecture, Japan. It occurs as a platy crystal and forms spherical aggregates. Hizenite-(Y) closely associates with lokkaite-(Y), tengerite-(Y), and kimuraite-(Y). It is orthorhombic, a = 6.295(1) Å, b = 9.089(2) Å, c = 63.49(1) Å, V = 3632(1) Å3, Z = 4. Hizenite-(Y) is white in color with vitreous to silky luster. The density is 2.98 g/cm3 (calc), and there is a perfect cleavage on {001}. The strongest lines in the X-ray powder diffraction pattern are [d (I/I0hkl] 10.63 (100) 006, 6.384 (77) 0·0·10, 3.962 (51) 0·0·16, 3.821 (27) 029, 1·0·13, 2.060 (23) 306, 0·4·13, 15.57 (20) 004.
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LETTERS
  • Shigeki TSUCHIYA, Takao HIRAJIMA
    Volume 108 (2013) Issue 3 Pages 166-171
    Released: July 04, 2013
    JOURNALS FREE ACCESS
    The lawsonite (Lws) eclogite facies mineral assemblage [Lws + omphacite (Omp)] was discovered as an inclusion in garnet (Grt) within a unique epidote (Ep)-glaucophane (Gln) eclogite in the Kotsu area of the Sanbagawa belt in eastern Shikoku, Japan. One of the unique characteristics of this eclogite is the occurrence of Grt, displaying a distinct Mn-bell shaped zoning pattern {Xsps [= Mn/(Fe2+ + Mn + Mg + Ca)] > 0.4 at the core}. Lws inclusions are columnar shaped crystals of ∼ 20 μm in size, and are present from the Outer Core to Inner Rim {0.03 < Xprp [= Mg/(Fe2+ + Mn + Mg + Ca)] < 0.08}. Omp inclusions are anhedral, 10-100 μm in size, and are present from the Inner Rim to Outer Rim (0.06 < Xprp < 0.11). The mineral assemblage of the unique eclogite in the matrix (i.e., Grt, Omp, Ep, quartz, Gln/barroisite, and phengite) is identical to that of the common eclogite in the relevant area. However, the Mn bell-shaped zoning of Grt is weak in the common eclogite (Xsps < 0.1 throughout the grain). Combining a model petrogenetic grid within the NCKFMASH system and paragenesis of inclusion minerals in the zoned Grt allowed us to propose a new prograde P-T path for the Kotsu eclogite [i.e., (1) ∼ 400 °C and 0.8 GPa represented by an assemblage of Lws + albite + Gln + Ep + paragonite (Pg) in the Inner Core, (2) a subsequent P and T increase from ∼ 450 °C and 1.3 GPa to 550 °C and 1.8 GPa by an assemblage of Lws + Omp + Gln + Ep + Pg in the Inner Rim, and (3) 600 oC and 2.0 GPa by an assemblage of Grt + Omp + Gln + Ep + Pg in the Outer Rim/matrix]. The derived prograde P-T path is comparable to the thermal structure along the top of the present-day Philippine Sea slab beneath Shikoku Island, as calculated by Peacock (2009).
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  • Hiroyuki KAGI, Shoko ODAKE, Hidemi ISHIBASHI, Katsumi SHOZUGAWA, Motoy ...
    Volume 108 (2013) Issue 3 Pages 172-177
    Released: July 04, 2013
    JOURNALS FREE ACCESS
    The valence state of chromium in ferropericlase inclusions within diamonds was expected to serve as a redox indicator applicable to the deep earth environment with an extremely reduced condition. In this study, Cr K-edge X-ray absorption near-edge structure (XANES) spectra and 57Fe Mössbauer spectra were obtained for ferropericlase samples synthesized under controlled oxygen fugacity conditions of -7, -9, and -11 in log fO2. All the ferropericlase samples were shown to have almost identical Fe3+/Fe2+ ratios; this observation is consistent with a phase diagram of ferropericlase reported previously. All the ferropericlase samples contained Cr2+, and the Cr2+/ΣCr ratio was almost constant among the samples, within the experimental precision of XANES spectroscopic measurements. Divalent chromium ions are stabilized in ferropericlase by the crystallographic constraint, even under an oxidized condition. The present study proposes that there is room for reconsidering the presence of Cr2+ in ferropericlase inclusions in diamonds as evidence of the extremely reduced condition of the lower mantle.
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  • Aya YOSHIMOTO, Yasuhito OSANAI, Nobuhiko NAKANO, Tatsuro ADACHI, Kazuh ...
    Volume 108 (2013) Issue 3 Pages 178-183
    Released: July 04, 2013
    JOURNALS FREE ACCESS
    The Kurosegawa Tectonic Zone, which is one of the least geochronologically understood areas of the Japanese Islands, contains several rock types of contrasting ages in a serpentinite mélange. This paper presents the U-Pb ages of detrital zircons in pelitic schists and quartzite from the Kurosegawa Tectonic Zone, where high-pressure/low-temperature metamorphic rock (e.g., blueschist) is one of the main constituents. We analyzed a variety of samples including glaucophane-bearing pelitic schist from the Itsuki area in Kyushu and the Toba area on the Kii Peninsula, and quartzite from the Anan area in eastern Shikoku. The U-Pb age distributions reflect similar characteristics for all three areas, indicating significant peaks at 450-500 Ma and ∼ 600 Ma, with additional scattered ages of 800-1800 Ma, and ages older than 2000 Ma. These results suggest that the provenance of the protolith of these high-pressure/low-temperature metamorphic rocks from the Kurosegawa Tectonic Zone would be the same between Kyushu and the Kii Peninsula through the Shikoku area. The distributions of detrital zircon ages in the Kurosegawa Tectonic Zone are similar to those from Permian-Triassic collision-related metamorphic rocks of the Ogcheon Metamorphic Belt and Gyeonggi Massif in South Korea, and from Devonian sedimentary rocks in the South China Craton.
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  • Kazuhiro YONEMURA, Yasuhito OSANAI, Nobuhiko NAKANO, Tatsuro ADACHI, P ...
    Volume 108 (2013) Issue 3 Pages 184-188
    Released: July 04, 2013
    JOURNALS FREE ACCESS
    The Mogok Metamorphic Belt (MMB), situated in central Myanmar, contains an assemblage of high-grade metamorphic rocks believed to have been formed during a regional Early Eocene-Oligocene metamorphic event. We newly found Grt-Opx granulite in the Mogok area, which was formed under pressure-temperature (P-T ) conditions estimated as being 6.5-8.7 kbar and 800-950 °C. Based on the results of EPMA U-Th-Pb Mnz dating, the central MMB, which runs through the Mogok, Mandalay, and Meikthila areas, is characterized by an Eocene to Oligocene deformation and fluid infiltration event. In addition, several Mnz grains from the Meikthila and Mandalay areas record ages of the Late Triassic (∼ 200 Ma) and Cretaceous (∼ 80 Ma and 110 Ma) geologic events.
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