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

本论文主要研究了以下三个方面的问题，并分别取得了以下研究成果：1.铝石榴石-钙钛矿相转变以天然石榴石为原料的激光加热金刚石压砧实验和回收样品的分析电子显微镜表明：1）虽然下地幔条件下的主要后石榴石相为斜方钙钛矿，但在一定的温度和压力条件下，也有一些富Al相和斯铁橄榄石与斜方钙钛矿共存，2）首次发现硅酸盐LiNbO_3相是由正交钙钛矿转变而来的亚稳相; 3）钙钛矿中Fe、Al、Ca含量之间存在正相关关系，且随压力的增大而增加.（Mg，Fe）SiO_3镁橄榄石的立方-四方相转变对多压砧合成镁橄榄石和天然陨石镁橄榄石的电子显微分析表明，合成镁橄榄石为四方相，天然镁橄榄石为立方相。合成镁橄榄石的显微结构表明，在20 GPa，-1900 ℃的高温下，立方相的稳定范围很宽。立方相和四方相之间的边界温度随Fe含量的增加而升高.高温高压下顽火辉石的相变同步辐射高温高压原位X射线衍射实验表明，正交PbCa高压侧存在较宽范围的单斜C2/c相。这种C2/c相的β角明显小于高温C2/c相的β角，表明这两个相是彼此不同的结构。单斜晶系P2_1/c在较低温度下可能具有介于正交晶系Pbca和单斜晶系C2/c之间的稳定域。

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.