Searching mineralogy of the Earth's deep interior using a combination of synchrotron radiation and high-pressure technology

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Technical developments have been made in producing higher pressures in multianvil apparatus using sintered diamond (SD) anvils and also for precise measurements of sound velocities of high-pressure phases under the P/T conditions of the mantle transition region. We succeeded to produce pressures as high as〜80 GPa at room temperature using SD anvils, while pressures have been limited to〜60 GPa at the high temperatures relevant to the Earth's mantle. Some new phase transitions have been found in mantle minerals under the conditions of the lower mantle, and precise determination of the P-V-T relations of these and other high-pressure phases have been conducted under the corresponding P, T conditions. On the other hand, precise measurements of sound velocities have been made at pressures to〜20GPa and temperatures to〜1700K, equivalent to those of the depths of the middle part of the mantle transition region. Using this technique; measurements on ringwoodite and majorite in a pyrolite composition, polycrystalline MgO, and the garnetite (majorite + stishovite) in a basaltic composition have been made, which provided important data sets to constrain the mineralogy of the mantle transition region and to provide a new self-consistent pressure scale. In addition to these studies, we have tested the performance of the newly produced nano-polycrystalline diamond (HIME-DIA) for high-pressure devices, and found the great potential of this novel material for anvils for both multianvil apparatus and diamond anvil cell, which yielded the highest pressures of〜110 Gpa and〜20 Gpa, respectively.