| Project/Area Number |
01460052
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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 |
固体地球物理学
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| Research Institution | Okayama University |
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Principal Investigator |
ITO Eiji Institute for Study of the Earth's Interior, Okayama University, Professor, 地球内部研究センター, 教授 (00033259)
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| Co-Investigator(Kenkyū-buntansha) |
AKIMOTO Shun-iti Institute for Study of the Earth's Interior, Okayama University, Professor (Reti, 地球内部研究センター, 教授 (50013462)
TAKAHASHI Eiichi Department of Earth and Planetary Sciences, Faculty of Science, Tokyo Institute, 理学部, 助教授 (40144779)
NAKAMURA Eizo Institute for Study of the Earth's Interior, Okayama University, Associate Profe, 地球内部研究センター, 助教授 (80201672)
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| Project Period (FY) |
1989 – 1991
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| Keywords | Post-spinel phase / Perovskite / Subducting slab / Deep earthquake / Superplastivity / Melting experiment / Core segregation / Evolution of the core |
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| Research Abstract |
The detailed phase diagrams of the olivine-modified spinel-spinel and the post spinel transformations, were constructed for the system Mg_2SiO_4-Fe_2SiO_4. The mantle spinel dissociates into perovskite (Pv) and magnesiowustite (Mw) within a depth interval less than 4 km making the 650 km discontinuity be sharp. This feature provide a fixed point of mantle temperature at 650 km depth and a standard temperature profile of the upper mantle was proposed. The dynamic nature of descending slabs was analyzed. The characteristics of deep focused earthquakes are well explained in terms of plunging and buoyant forces acting on the slabs caused by the distortions of phase boundaries. It was also pointed out that the sudden disappearance of seismic activity around 700 km depth would be due to the superplasticity associated with the breakdown assemblage of Pv and Mw.
Results of subsolidus and melting experiments on MgCO_3 and the system MgCO_3-MgSiO_3 conducted up to 25 GPa and 2000 ﾟC revealed that
… More
, in the depths greater than 140 km, CO_2 no longer behaves as a volatile component but is fixed as magnesite, and that CO_2 is progressively released into the atmosphere by the igneous process. Examination of the solubility of CO_2 into H_2O fluid at high P and T made it possible to discuss the recycling process of CO_2 by taking the subduction into consideration.
Extensive effort was focused on the melting relations of the lower mantle materials. MgSiO_3 Pv melts congruently at about 2500 ﾟC and 23 GPa with a dTm/dP slope of about 25ﾟ/GPa. The melting reration of the MgO-FeO-SiO_2 system exhibits a eutectic melting between Pv and Mw. It should be noteworthy that the eutectic composition is richer in SiO_2 than that found in the conditions of the transition zone and the composition is enriched in SiO_2 under further increase of depth. Melting experiments were extended to the core materials. It was demonstrated that SiO_2 component dissolves into molten iron from silicate melts at pressures higher than 15 GPa and the dissolution is enhanced by the increasing pressure. It was shown that potassium, a possible candidate as heat source in the core, also dissolves into molten iron. These results make it possible to construct a core formation model which consistently account for the light elements of the outer core, and the evolution of the core and the formation of the D^1 layer associated with cooling of the earth. Less
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