Abstracts for Annual Meeting of Japan Association of Mineralogical Sciences
2012 Annual Meeting of Japan Association of Mineralogical Sciences
Showing 1-50 articles out of 253 articles from the selected issue
S1: Mineralogical researches for elucidating toxic elements behavior related to 311 earthquake and Fukushima power plant accident
S2: Water Rock interaction
S3: Fluids in igneous processes
  • Yoshitaka Kumagai, Tatsuhiko Kawamoto, Junji Yamamoto
    Session ID: S3-01
    Published: 2012
    Released: June 10, 2014
    CONFERENCE PROCEEDINGS FREE ACCESS
    We investigate chemical compositions of fluid inclusions in amphibole-bearing spinel-plagioclase lherzolite xenoliths of the Ichinomegata volcano, northeast Japan arc. The fluid inclusions are composed of CO2H2OClS fluids. The salinity of fluid inclusions is 0.18–0.35 and 3.7 wt% NaCl equivalent. Assuming that these fluid inclusions have originated from a vapor-saturated basaltic magma, H2O and CO2 contents of the magma coexisting with the fluids preserved as fluid inclusions are 2.95.3 wt% H2O and 0.70.8 wt% CO2, respectively. The Cl content of the magma is 0.020.05 wt%.
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  • Takeshi Kuritani, Jun-Ichi Kimura, Eiji Ohtani, Hideaki Miyamoto, Kats ...
    Session ID: S3-02
    Published: 2012
    Released: June 10, 2014
    CONFERENCE PROCEEDINGS FREE ACCESS
    The origin of historic potassic basalts (from the 1719–1721 AD eruption) from the Wudalianchi volcanic field, northeast China, is investigated. The samples contain ~5 vol.% olivine microphenocrysts, and are characterized by K2O enrichment (>4 wt.%) and an EM1-like isotopic signature. By using thermodynamic calculations with the observed petrological features of the basalts, the eruption temperatures of the magmas are estimated to have been about 1250–1260°C. Because the estimated temperatures are significantly higher than the estimated maximum temperature of the lithospheric mantle beneath the Wudalianchi volcanic field, the magmas have plausibly been derived from the asthenospheric mantle. We suggest that both the potassic- and EM1-like natures of the basalts originated from the mantle transition zone which was metasomatized by K-rich sediment fluids at ~1.5 Ga ago through a stagnation of an ancient slab. We infer that the Wudalianchi magmatism was caused by an upwelling of a hydrous mantle plume from the mantle transition zone which has been remarkably hydrated through stagnation of the ancient subducted slab and the recent Pacific slab.
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  • Hitomi Nakamura, Hikaru Iwamori
    Session ID: S3-03
    Published: 2012
    Released: June 10, 2014
    CONFERENCE PROCEEDINGS FREE ACCESS
    The melting conditions have been estimated inversely by optimizing the predicted magma composition to the observed composition of volcanic rock, with the two parameters: melting degree and the proportion of spinel- and garnet-lherzolite involved in melting. Consequently, the low melting degree of dominantly garnet-lherzolite with a high fluid flux from the two slabs beneath central Japan has been argued to be responsible for compositional characteristics, including the adakitic signatures, of the studied rocks. These results imply that the geochemical approach may provide a useful constrain to the P-T condition in the mantle wedge to constrain the geothermal structure in subduction zones.
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  • Morihisa Hamada, Toshitsugu Fujii
    Session ID: S3-04
    Published: 2012
    Released: June 10, 2014
    CONFERENCE PROCEEDINGS FREE ACCESS
    We analyzed OH concentration of plagioclase inMORB from Indian Ocean to constrain partitioning of H between plagioclase and low-H2O basaltic melt. The OH concentration of plagioclase was ≤ 60 wt. ppm H2O and H2O concentration of plagioclase-hosted melt inclusions was ≈0.05 wt.%. As a result, partition coefficient of H between plagioclase and basaltic melt is ≈ 0.1 in molar basis under almost dry conditions. This analytical result is consistent with our previous experiments on hydrogen partitioning between plagioclase and H2O-undersaturated melt, where partition coefficient is highest under almost dry conditnin and monotonously decreases with increasing H2O in melt. 
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  • Eiichi Takahashi, Morihisa Hamada, Masashi Ushioda, Kenta Asano
    Session ID: S3-05
    Published: 2012
    Released: June 10, 2014
    CONFERENCE PROCEEDINGS FREE ACCESS
    We studied water content in basalt magma from Izu-oshima, Miyakejima and Fuji volcanoes, based on petrology, OH in minerals, melt inclusions and experimental constrints on magma chambers, etc. We found that arc tholeiite basalt magma contains 3-5 wt% of water at crustal magma chamber depper than 10 km beneath these volcanoes. We show that changing lithology, fractionation trends and style of volcanic activity are largely controlled by the water content and the mode of degassing from the magma.
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  • Hidemi Ishibashi, Shoko Odake, Kyoko Kanayama, Morihisa Hamada, Hiroyu ...
    Session ID: S3-06
    Published: 2012
    Released: June 10, 2014
    CONFERENCE PROCEEDINGS FREE ACCESS
    Fe3+/ΣFe ratios were measured for quenched boninitic and basaltc glasses erupted at the early stage of Ogasawara arc formation by using Fe-K edge micro-XANES spectroscopy. Boninitic and basaltic glasses showed Fe3+/ΣFe ratios of 0.2-0.25 and 0.18-0.22, which correspond to ΔQMF values [=log fO2 - log fO2 (QMF)] of 1-1.7 and 0.6-1.2, respectively; the boninitic glasses were slightly more oxidized than the basaltic ones. ΔQMF values inferred for their primary melts were almost identical; 0.4-1.1 and 0.4-0.8, respectively, which are more oxidized than MORB glasses. We will discuss about fO2 development process of arc mantle based on the present results.
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  • Keiko Matsumoto, Michihiko Nakamura
    Session ID: S3-07
    Published: 2012
    Released: June 10, 2014
    CONFERENCE PROCEEDINGS FREE ACCESS
    Pyrrhotite (Po) in the pumice from the Sakurajima Taisho eruption is sometimes partly reacted to form spongy Fe oxides. EPMA analyses revealed that they are mostly magnetite. Even in the outermost rim, they contain no Ti, showing that the spongy magnetite contacted with melt in less than 4 h before quenching. Thermodynamic calculations showed that the upper limit of the Po–stable fO2 is NNO +2.6 log unit at magmatic temperature. These observations indicate that the reaction was caused at a shallow volcanic conduit during eruption. The desulfidation reaction of Po may be used as a geospeedometer in explosive eruptions.
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  • Xianyu Xue, Masami Kanzaki
    Session ID: S3-08
    Published: 2012
    Released: June 10, 2014
    CONFERENCE PROCEEDINGS FREE ACCESS
    The mechanism of water dissolution in silicate melts and glasses is an important factor governing its effects on their physical and thermodynamic properties. Our previous studies have revealed that for Ca-Mg silicate melts (glasses), both SiOH and free OH (e.g. MgOH), whose formations have opposite effects on the network structure and viscosity, are present. Whether free OH also occurs in hydrous alkali silicate systems has been controversial. Here we demonstrate from a combined 1H MAS NMR and double-resonance (29Si-1H and 23Na-1H) NMR study that water dissolves predominantly as SiOH and molecular H2O in Na silicate melts (glasses).
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  • Shumpei Yoshimura, Michihiko Nakamura , Hisayoshi Yurimoto
    Session ID: S3-09
    Published: 2012
    Released: June 10, 2014
    CONFERENCE PROCEEDINGS FREE ACCESS
    The carbon isotopic fractionation between CO2-rich fluid and granitic melt was determined to be Δf-m = +0.8‰ at 1200 °C and 10 kbar. Infrared spectrometry revealed that both CO2 molecule and CO32- are present in this melt. The carbon isotope fractionation is modelled as a linear function of the ratio of CO3-2 to CO2molecule.
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R1: Characterization and description of minerals
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