Journal of Mineralogical and Petrological Sciences
Online ISSN : 1349-3825
Print ISSN : 1345-6296
ISSN-L : 1345-6296
Volume 106 , Issue 5
October
Showing 1-6 articles out of 6 articles from the selected issue
ORIGINAL ARTICLES
  • Changqiu WANG, Ruochen YANG, Yan LI, Cuie XIONG, Wenwen ZHAO, Jianying ...
    2011 Volume 106 Issue 5 Pages 229-234
    Published: 2011
    Released: November 09, 2011
    [Advance publication] Released: October 19, 2011
    JOURNALS FREE ACCESS
    Psammoma bodies (PBs) in meningioma patients often contain mineral deposits. In this paper, the mineralogical characteristics of PBs in the mineralized focus in meningioma patients were investigated by using scanning electron microscopy (SEM), environmental scanning electron microscopy (ESEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray analysis (EDAX), and electron probe microanalysis (EPMA). We found that PBs had a concentric layered structure and the size ranged from several to tens of micrometers. Although no obvious trend in the variation of Ca/P ratios was observed from the center to the outer edge of the PBs, the Ca/P ratios were much lower in the early stage of PBs formation. The concentric layered structure of the PBs might be formed by a spiral arrangement of mineralized collagen fibers. Studies on PBs mineralization may provide some supporting information in understanding the origin and development of meningiomas.
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  • Khadidja ABBOU-KEBIR, Shoji ARAI, Ahmed HASSAN AHMED, Georges CEULENEE ...
    2011 Volume 106 Issue 5 Pages 235-245
    Published: 2011
    Released: November 09, 2011
    [Advance publication] Released: October 19, 2011
    JOURNALS FREE ACCESS
    Enigmatic dunitic veins and veinlets crosscutting a podiform chromitite ore body discovered in Wadi Rajmi, northern Oman ophiolite, display a peculiar characteristic of being almost or completely spinel-free. Olivines show an evolution trend from the spinel-free dunites (Fo93-94 and 0.4 wt% NiO) to the spinel-bearing dunites (Fo91-93 and 0.2-0.3 wt% NiO). The Cr/(Cr + Al) of chromian spinel grains increases from 0.6 to 0.8, accompanied by a slight increase in Fe3+ ratio, and the Fo content of olivine decreases in the spinel-bearing dunites. A high-Mg magma, initially undersaturated with chromian spinel, precipitated the spinel-free dunites. Once the spinel saturation of the melt was attained by fractionation, the spinel-bearing dunites precipitated. The initial magma was possibly komatiitic in nature, which was produced at an early stage of detachment of the oceanic lithosphere that formed the Oman ophiolite.
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  • Terumi Ejima, Masahide Akasaka, Hiroaki Ohfuji
    2011 Volume 106 Issue 5 Pages 246-254
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    The oxidation state and distribution of Fe in olivine in a lherzolite xenolith from the Oku district, Oki-Dogo Islands, Japan, were investigated. A lherzolite xenolith collected from a volcanic neck of alkali olivine basalt contains olivine, orthopyroxene, clinopyroxene, and a small amount of spinel. Anhedral anorthite grains less than 0.01 mm across occur as inclusions in clinopyroxene. The olivine grains are nearly homogeneous in composition, with Fo contents of 80.7-81.9 mol%. Pure olivine grains for X-ray diffraction and 57Fe Mössbauer analyses were separated from the fresh core of the lherzolite xenolith under a binocular microscope. The Mössbauer spectrum of the separated olivines consists of two doublets assigned to Fe2+ at the M1 and M2 sites and a doublet attributed to Fe3+ at the M2 site. The populations of Fe3+ in the olivine derived from the Mössbauer method and FeLβ/FeLα-intensity ratios are 0.02 and 0.03 atoms per formula unite (apfu), respectively. The site occupancies of Fe in the M1 and M2 sites refined using X-ray Rietveld method are 0.151 and 0.206 apfu, respectively. The chemical formula of the olivine based on the refined Fe populations at the octahedral M1 and M2 sites and oxidation state of Fe determined using Mössbauer method is [M2(Mg2+0.79Fe2+0.19Fe3+0.02)M1([]0.01Mg0.85Fe2+0.14)]Σ2.00SiO4.
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LETTER
  • Mohamed Zaki Khedr, Shoji Arai
    2011 Volume 106 Issue 5 Pages 255-260
    Published: 2011
    Released: November 09, 2011
    [Advance publication] Released: October 15, 2011
    JOURNALS FREE ACCESS
    The Ise area is located in the western part of the Hida Marginal Belt (central Japan), which includes several sporadic exposures of ultramafic rocks, sometimes forming a serpentinite mélange of the Paleozoic age. Ultramafic rocks in the Ise area, enveloped by Paleozoic-Mesozoic sedimentary rocks, are completely serpentinized; however, the abundance of bastite after orthopyroxene suggests harzburgite protoliths. The bastite- and mesh-textured serpentines are distinguished from each other in Al2O3, Cr2O3 and NiO contents. The bastite-textured serpentine is high in Al2O3 (up to 4.0 wt%) and Cr2O3 (up to 1.2 wt%), but low in NiO (<0.3 wt%) relative to the mesh-textured one. Relic chromian spinel, vermicular in shape, shows an inter-grain chemical homogeneity and is sometimes altered to ferritchromite at the margin. It has a narrow range of Cr# [= Cr/(Cr + Al) atomic ratio] from 0.38 to 0.51 and low YFe {=[Fe3+/(Cr + Al + Fe3+) atomic ratio, <0.03]}, similar to chromian spinel in Kotaki and Oeyama ultramafic masses. It is also similar in chemistry to spinels in forearc and abyssal peridotites, suggesting two possibilities for the derivation of the Ise serpentinite's protoliths. The degree of melting using Cr# versus TiO2 of chromian spinel is ∼ 20-25%, which is in accordance with the harzburgite protoliths obtained by whole-rock chemistry models. We found that Cr, Al, Ni and Ca, preserved in bastite and mesh-textured serpentine, are conservative during serpentinization, confirmed from the similarity in the whole-rock A1 and Ca of the Ise serpentinites to Horoman harzburgites. The occurrence of dolomite can stabilize the Ca and limited its mobility to escape outside the serpentinites. The harzburgite protoliths were possibly serpentinized by slab-derived fluids at a shallow depth relative to the Happo-O'ne serpentinites during the exhumation process.
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  • Norikatsu AKIZAWA, Shoji ARAI, Akihiro TAMURA, Jiro UESUGI, Marie PYTH ...
    2011 Volume 106 Issue 5 Pages 261-266
    Published: 2011
    Released: November 09, 2011
    JOURNALS FREE ACCESS
    This paper details a new discovery of anorthite-bearing diopsidites (= anorthite diopsidites) from the lowermost crust along Wadi Fizh in the northern Oman ophiolite. The anorthite diopsidites occur as networks within layered gabbros 50 m above the gabbro/peridotite boundary, and are mainly composed of high-Mg diopsidic clinopyroxenes and anorthites with various amounts of uvarovite. They are intermediate in mineral chemical characteristics between the crustal gabbros and the diopsidites, and interpreted as an interaction product between high-temperature Ca-rich hydrothermal fluids and peridotites within the mantle section. The anorthite diopsidites were probably formed by interaction between the fluids involved in diopsidization within the mantle section and the layered gabbro. The fluids responsible for the formation of the anorthite diopsidite were also Ca-rich and carried Cr to form uvarovite from the underlying mantle section. High-temperature hydrothermal circulation plays an important role in the transportation of elements, e.g., Ca and Cr, from the upper mantle to the lower crust across the Moho in the ocean floor.
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Mineralogical abstracts from scientific papers published in Japan
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