An Experimental Study on Early Evolution of the Earth and the Structure of the Lower mantle

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We have continued experiments to generate higher pressures using the Kawai-cell equipped with sintered diamond anvils at synchrotron Spring-a The generated pressure reached 85 GPa at room temperature and 87 GPa at 1000 K on the Anderson et a〓s au male Based on these innovations of experimental techniques, we have systematically examined the penovskite (Pv) -postperovskite (PPv) transformation in MgGeO_3 up to 74 GPa and 1900 K. The starting material was a fine mixture of MgGeO_3 ilmenite + 0.1 Au (in weight), which was directly loaded in a cylindrical TiB_2 heater set with a thin W/W-Re thermocouple at the center of a mall octahedral pressure medium of MgO +0.05Cr_2O_3 (in weight). Pressure value was determined form measured volume of Au from the Anderson at a〓s scale. The transformation from Pv to PPv was first confirmed at 63.2 GPa and 1323 K. Then we tried to observe the reversal reaction by decreasing pressure and keeping temperature constant Growth of Pv was not recognized until p … More ressure went down to 60.5 GPa., suggesting the reversal reaction to be fitly sluggish The second transformation to PPv from the reversed Pv was observed at 62.8 GPa and 1473 K by heating. In the next run, it was found that well crystalline Pv persisted to pressures much higher than the expected Pv-PPv phase boundary, and growth of PPv was first recognized at 74 Gpa and 1873 K Taking the slow reaction rate in to consideration, we observed the growth of the Pv and PPv and the coexistence of both the phases in the 3rd nut The run. The phases boundary thus determined is expressed by the equation; T (K) = 191.2P (Gpa) -10563. If dP/dT slope of the phase boundary obtained in the present study for MgGeO_3 were applicable to the Pv-PPv transformation in the mantle, the PPv would be suppressed to the bottom the lower mantle, and on called PPv lens may not form. We have also pointed out that the establishment of reliable pressure scale is urgent issue of high pressure Earth science.In order to overcome faults of the DIA type press in squeezing the Kawai-cell, we have developed a new 6-axis apparatus in which movement of the six anvils are controlled by the high tech servo mechanism. It is possible to keep the Ka wai-cell cubic within accuracy of ± 2 μm. Pressure generation using sintered diamond cubic anvils was carried out up to ca. 60 GPa by measuring electrical resistance of GaP, Zr, and Fe_2O_3. The results are compared with the previous calibration performed at Spring-8 by means of in situ X-ray observation. It is demonstrated that significant amount of applied load is balanced with frictional force in the DIA type press. The load loss amounts to 45 % at ca. 60 Gpa.Electrical conductivity of wadsleyite and ringwoodite with composition of (Mg〓Fe0.1)_2SiO_4 was measured up to 20 Gpa and 2000K under both anhydrous and hydrous conditions. Measurement over the wide temperature range made it possible to determine the parameters for hopping and proton conduction mechanisms for both the materials. These results imply that electrical conductivity of the mantle transition zone (depths from 410 to 660 km) determined by the geomagnetic measurement is well reconciled anhydrous wadsleyite and ringwoodite and hypothesis of wet transition zone is ruled out. Less