Experimental study on the melting relation of silicate under the lowermost mantle condition

点击翻译按钮获取中文摘要

In this research project, we investigated the phase relation of the minerals under the lowermost mantle condition and the chemical reaction between those minerals and molten iron up to the condition corresponding to the earth's core-mantle boundary. For realizing such extreme conditions, we newly designed a symmetrical diamond anvil cell with a wide conical window for laser-heating and optical spectroscopy. The laser-heating system was also refined for stable heating and optimal temperature measurement from the hot sample by a spectroradiometric method. Experiments were performed using these techniques at SPring-8 and Photon Factory for in-situ X-ray diffraction measurements at high P-T, and also at laboratory for recovery runs to check the quenched samples. Thanks for the recent advances in micro-processing technologies such as laser cutting, focused ion beam, we successfully prepared the thin section of the recovered samples for analytical transmission electron microscopy. Finally we … More obtained the following results. (1) The chemical reaction between molten iron and perovskite and post-perovskite phase and wetting property at the core-mantle boundary condition was examined, and silicon and oxygen turned to be important candidates as light elements in the outer core. The wetting angle between post-perovskite phase and molten iron was slightly higher than the critical angle of 60°, which means 2wt% of the core material can be trapped in the D" layer. (2) Magnesiowustite is the heaviest minerals overall the mantle based on the iron partitioning experiments between magnesium oxide and silicate perovskite and post-perovskite phase. No evidence for the effect of a high-spin to low-spin transition was found in these minerals. (3) Potassium can be dissolved into molten iron significantly at core-mantle boundary condition, and the element may work as a heat source in the core. (4) The hydrous mineral, delta-AIOOH, has a wide stability field over 100GPa and 2000K, therefore this phase at relatively low temperature condition in descending slab possibly survive to the lowermost mantle to supply the water to core-mantle boundary. (5) Potassium bearing silicate with post-hollandite structure can be stably exist at the lowermost mantle condition. Less