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

在本研究项目中，我们研究了地幔最下层条件下矿物的物相关系，以及这些矿物与铁水之间的化学反应，直至对应于地球核幔边界的条件。为了实现这种极端条件，我们新设计了一个对称的金刚石砧细胞，具有宽锥形窗口，用于激光加热和光学光谱。对激光加热系统进行了改进，使其能够稳定加热，并通过光谱辐射法对热样品进行最佳温度测量。实验使用这些技术在SPring-8和Photon Factory进行了高P-T的原位x射线衍射测量，并在实验室进行了回收运行以检查淬火样品。由于激光切割、聚焦离子束等微加工技术的最新进展，我们成功地制备了回收样品的薄片，用于分析透射电子显微镜。最后，我们……More得到了以下结果。(1)考察了铁液与钙钛矿的化学反应、后钙钛矿相以及在核幔边界条件下的润湿性质，硅和氧成为外核轻元素的重要候选者。后钙钛矿相与铁水之间的润湿角略高于60°的临界角，这意味着2wt%的芯材可以被困在D”层中。(2)氧化镁与硅酸盐钙钛矿及后钙钛矿相的铁配分实验表明，镁武铁矿是整个地幔中最重的矿物。在这些矿物中没有发现高自旋到低自旋转变的证据。(3)钾元素在地核-幔边界条件下能明显溶解于铁水中，并可能在地核中起热源作用。(4)含水矿物三角洲- aiooh具有100GPa和2000K以上的宽稳定场，因此这一阶段在下降板块温度相对较低的条件下可能存活到最底地幔，为核幔边界供水。(5)后荷兰岩结构的含钾硅酸盐可稳定存在于最下层地幔条件。少

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