| Project/Area Number | 08404034 |
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Petrology/Mineralogy/Science of ore deposit
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| Research Institution | Gakushuin University |
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Principal Investigator |
AKAOGI Masaki Gakushuin University, Department of Chemistry, Proffesor, 理学部, 教授 (30126560)
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| Co-Investigator(Kenkyū-buntansha) |
NAGASAWA Hiroshi Gakushuin Unversity, Department of Chemistry, Professor, 理学部, 教授 (80080464)
SUZUKI Toshihiro Gakushuin Unversity, Department of Chemistry, Research Associate, 理学部, 助手 (40235974)
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| Project Period (FY) |
1996 – 1998
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| Project Status |
Completed(Fiscal Year 1998)
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| Budget Amount *help |
¥38,300,000 (Direct Cost : ¥38,300,000)
Fiscal Year 1998 : ¥3,400,000 (Direct Cost : ¥3,400,000)
Fiscal Year 1997 : ¥5,000,000 (Direct Cost : ¥5,000,000)
Fiscal Year 1996 : ¥29,900,000 (Direct Cost : ¥29,900,000)
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| Keywords | high pressure experiment / calorimetry / mantle / garnet / perovskite / silicate melt / element partitioning / 熱測定 / スピネル / ガ-ネット |
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| Research Abstract |
Phase equilibria of mantle minerals and partitioning between silicate melt and the minerals were clarified by means of high pressure experiments and calorimetry in order to shed light to constitution and chemical evolution of the mantle. The importnat results obtained in this project are described below.
1. Dissciation boundaries of spinel in the system Mg_2SiO_4-Fe_2SiO_4 were determined, and calorimetric measurements of perovskites in the system MgSiO_3-FeSiO_3 were performed. The post-spinel transition boundaries calculated using the above data indicate that the spinel dissociation boundary to perovskite and magnesiowustite has a slope of-3*1MPa/K and that Mg-rich spinel first dissociates into magensioswustite and stishovite at relatively low temperatures.
2. Mg_3Al_2Si_3O_<12>, garnet dissociates at 27 GPa into perovskite and corundum, which combine into a single phase perovskite at 37 GPa. In the system Mg_4Si_4O_<12>-Mg_3Al_2Si_3O_<12> garnet solid solution transforms to perovskite
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via the two-phase field. These results indicate that host phase of Al in the lower mantle is perovskite. The garnet-perovskite transition boundary has a slope of 2* 1MPa/K, which enhances mantle convection. Fe_3Al_2Si_3O_<12> garnet dissociates into component oxides at 21 GPa.
3. A new Mg-rich hexagonal phase was found in the system CaAl_2O_4-MgAl_2O_4, and the structure was determined. It is concluded that unknown Al-rich phases observed in previous studies on high pressure experiments of natural garnet and MORB have the same structure as the newly found hexagonal phase.
4. Complete solid solutions of perovskite are stable in the system CaTiO_3-CaSiO_3 at above 15 GPa. The perovskites with less than 66 mol% CaSiO_3 were successfully recovered to ambient conditions. Based on calorimetric measurements of the recovered perovskites, enthalpy of CaSiO3perovskite was estimated and used to determine the dissociation boundary of CaMgSi_2O_6 pyroxene.
5. In the element partitioning experiments between silicate melt and minerals, chemical equilibrium in respect to all the elements was achieved in the experiments longer than 1 hour. The partition coefficients (D) between melt and olivine or magnesiowustite showed a maximum at around 65 pm of ionic radius. The D values between melt and garnet showed almost similar values in the range of 40-90 pm, above which they suddenly descreased. The D values between melt and CaSiO_3 perovskite showed two maxima at about 50 and 100 pm, and a minimum was present between them. Less
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