Pressure generation in the Kawai-type multianvil apparatus and rheology of the Earth's interior

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  • 川井型装置での圧力発生と地球内部のレオロジー
  • 日本鉱物科学会賞第21回受賞者 受賞記念研究紹介 川井型装置での圧力発生と地球内部のレオロジー
  • ニホン コウブツ カガクカイショウ ダイ21カイ ジュショウシャ ジュショウ キネン ケンキュウ ショウカイ カワイガタ ソウチ デ ノ アツリョク ハッセイ ト チキュウ ナイブ ノ レオロジー

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Abstract

<p>In this paper, I introduce three topics of my researches including the technical development of high pressure generation in the Kawai-type multianvil apparatus and rheological studies for the lower mantle and the inner core, as follows: (i) We extended the attainable pressure of the Kawai-type multianvil apparatus to 120.3 GPa at room temperature by equipping sintered diamond cubic anvils. In the experiments, however pressure dropped to 105 GPa from 120 GPa at 1673 K and we did not observe the phase transition from bridgmanite to post-perovskite. (ii) The electrical conductivity of mantle rocks during phase transformation from ringwoodite to silicate perovskite and ferro-periclase was measured at 25 GPa and 1300-1900 K. The electrical conductivity was high at the early stage of annealing, suggesting that ferro-periclase forms interconnected layers in aggregates of bridgmanite and ferro-periclase. At the later stage, the electrical conductivity decreased and reached to that of bridgmanite, suggesting the cut-off of the interconnected ferro-periclase because of rounding of crystals. The interconnection of ferro-periclase, which has a lower viscosity than bridgmanite, can be maintained in a cold descending slab over geological time scales (~ 1 My), indicating that a colder slab is less viscous than the warmer mantle surrounding it. The low-viscosity slab can be prevented from penetrating into the deeper part of the lower mantle by the high viscosities encountered at a depth of ~ 1000 km, that cause stagnation at this depth as observed by seismic tomography. (iii) A formation age of the inner core is a key to understanding Earth's evolution and its thermal history. Knowledge of grain size of the inner core material can provide a constraint of formation age of the inner core. We determined grain growth rate of ε-iron at ~ 55 GPa and 1200-1500 K by means of in-situ X-ray diffraction observation. Extrapolation of the grain growth law of ε-iron to the inner core conditions suggests that at least ~ 2.9 Gy is required to reach the equivalent size of the inner core inferred from seismology. Based on the translation model of the inner core, the present result indicates that the age of the inner core is older than 2.9 Gy.</p>

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