1988 Fiscal Year Final Research Report Summary
Phase Relations in the System CaO-MgO-Al_2O_3-Cr_2O_3-SiO_2 at high pressures and temperatures.
| Project/Area Number |
62460055
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
鉱物学(含岩石・鉱床学)
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| Research Institution | TOHOKU UNIVERSITY |
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Principal Investigator |
ONUMA Kosuke Faculty of Science, Tohoku University, 理学部, 教授 (50000865)
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| Co-Investigator(Kenkyū-buntansha) |
FUJIMAKI Hirokazu Faculty of Science, Tohoku University, 理学部, 助手 (90133933)
YOSHIDA Takeyoshi Faculty of Science, Tohoku University, 理学部, 助手 (80004505)
AOKI Ken-ichiro Faculty of Science, Tohoku University, 理学部, 教授 (00004276)
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| Project Period (FY) |
1987 – 1988
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| Keywords | Petrologic Model / Chromium / Lherzolite / Mantle / Phase Equilibria / Pyroxene / Plagioclase / 微量元素 |
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| Research Abstract |
In the present study following resutls have been obtained.
(1) The effect of Cr on phase relations in the system Mg_2SiO_4-CaAl_2Si_2O_8-CaMgSi_2O_6-SiO_2, an important petrologic model, has been studied at 1 atm in air. Addition of minor amount of Cr (Cr_2O_3= 0.24 wt.%) gives a significant effect on the phase relations. The phase assemblage olivine + orthopyroxene + clinopyroxene + spinel, which is not stable in the Cr-free system, is observed. This assemblage corresponds to that of spinel lherzolite. The facts obtained indicate that the presence of very small amount of Cr lowers the transformation temperature from plagioclase lherzolite to spinel lherzolite.
(2) Since the phase relations of the system MgSiO_3-CaAl_2Si_2O_8 has been problematical, detailed reexamination was carried out, before the study of the effect of Cr in this system. The orthopyroxene present in this system does not have a composition on join MgSiO_3-CaAl_2Si_2O<@23 and the assemblage of olivine + orthopyroxene + anorthite + liquid has some temperature range, indicating that the syste is not ternary but belongs to quaternary system.
(3) The experiments on the join CaMgSi_2O_6-Mg_2SiO_2-CaAl_2Si_2O_8-0.2% MgCr_2O_4 has been performed at 10 kbar to understand the effect of Cr on the silicate system under high pressures. The primary field of clinopyroxene is enlarged and that of spinel is decreased compared with that in the Crfree system. This phenomena are probably due to the partitioning of trace element among the crystalline phases and liquid. More detailed studies are needed to understand this problem.
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