下部マントルの流動特性 [in Japanese] Rheological Properties of the Lower Mantle [in Japanese]
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The earth's lower mantle is mainly composed of (Mg, Fe) SiO<SUB>3</SUB> perovskite and (Mg, Fe) O magneSiOwustite. It is essential to determine the rheological properties of MgSiO<SUB>3</SUB> perovskite and periclase for understanding the rheology of the lower mantle. High pressure and temperature experiments were carried out under lower mantle conditions to determine their rheological properties. The grain growth rates of perovskite and periclase were determined to be G<SUP>10. 6</SUP> [m] = 1×10<SUP>-57. 4</SUP>t [sec] exp (-320. 8 [kJ/mol] /RT) and G<SUP>10. 8</SUP> [m] =1×10<SUP>-62. 3</SUP>t [sec] exp (-247. 0[kJ/mol]/RT), respectively, where G is grain size at time t, R is the gas constant and T is the absolute temperature. The lattice diffuSion coefficient (D<SUB>1</SUB>) and grain boundary diffuSion coefficient (D<SUB>gb</SUB>) of silicon in MgSiO<SUB>3</SUB> perovskite were determined at 25GPa and 1673-2073 K to be D<SUB>1</SUB> [m<SUP>2</SUP>/sec] = 3. 76×10<SUP>-10</SUP>exp (-338 [kJ/mol] /RT) and δD<SUB>gb</SUB> [m<SUP>3</SUP>/sec] =1. 02×10<SUP>-16</SUP>exp (-303 [kJ/mol]/RT), respectively, where δ is the width of the grain boundary. The grain size of perovskite in the lower mantle is estimated to be 1-10 mm, which suggests diffusion creep (Nabarro-Herring creep) as a dominant deformation mechanism in the greater part of the lower mantle. The present results indicate that the subducting slab is much softer than the surrounding lower mantle due to the slow grain growth rate.
- The Review of High Pressure Science and Technology
The Review of High Pressure Science and Technology 9(1), 19-25, 1999-02-20
The Japan Society of High Pressure Science and Technology