Phase transformation and rheology of minerals in the Earth's crust and mantle

对以下三个主题进行了深入研究，分别得到了以下结果：铝石榴石-钙钛矿相变激光加热金刚石砧细胞实验以天然石榴石为起始材料，回收样品的分析电镜显示如下结果；(1)下地幔条件下的后石榴石相主要为正方晶钙钛矿，但随着温度和压力的变化，也有富Al相和钙钛矿与正方晶钙钛矿共存；(2)首次发现由正方晶钙钛矿转变为亚稳相的硅酸盐LiNbO_3相；(3)钙钛矿中Fe、Al和Ca含量呈正相关关系，且随压力的增加呈增加趋势。（Mg, Fe） SiO_3多数石的立方-四方转变多砧细胞合成多数石和天然陨石多数石的分析电镜显示，合成多数石为四方，而天然多数石为立方。合成多数石的显微结构表明，在20 GPa -1900℃以上的高温下，立方相的稳定范围较宽。立方相和四方相的边界温度随铁含量的增加而升高。高温高温下长辉石的相变同步辐射原位x射线衍射实验表明，正交Pbca高压侧单斜C2/c相存在较宽的稳定范围。该C2/c的β值明显小于高温C2/c的β值，说明这两相是不同的结构。单斜P2_1/c在较低温度下有可能具有介于正交Pbca和单斜C2/c之间的稳定场。

Three following subjects were intensively studied and the following results were obtained, respectively.1. Aluminous garnet-perovskite phase transformationLaser-heated diamond anvil cell experiments using natural garnets as starting materials, and analytical electron microscopy of the recovered samples showed the following results ; 1) although the main post-garnet phase under the lower mantle condition is orthorhombic perovskite, some Al-rich phase (s) and stishovite coexist with orthorhombic perovskite depending on temperature and prssure, 2) the silicate LiNbO_3 phase was found for the first time as a metastable phase transformed from the orthorhombic perovskite, 3) there are positive correlations between Fe, Al and Ca contents in perovskite, and these contents tend to increase with pressure.2. Cubic-tetragonal transition in (Mg, Fe) SiO_3 majoriteAnalytical electron microscopy of the synthetic majorite by multi anvil cell and the natural meteorite majorite showed that the synthetic majorite is tetragonal, while natural majorite is cubic. Microstructures of synthetic majorites indicate the wide stability range of cubic phase at higher temperatures thah-1900ﾟC at 20 GPa. The boundary temperature between cubic and tetragonal phases increases with Fe content.3. Phase transition of enstatite under high pressure and hihg temperatureHigh temperature and high pressure in situ X-ray diffraction experiments using synchrotron radiation showed that there exists a wide stability range of monoclinic C2/c phase on the high pressure side of orthorhombic Pbca. The beta anble of this C2/c is signficantly smaller than that of high temperature C2/c, indicating that these two phases are the different structures with each other. There is a possibility that monoclinic P2_1/c has a stability field between orthorhombic Pbca and monoclinic C2/c at lower temperatures.