High pressure phase equilibria of constituent minerals of mantle and oceanic crust, and chemical heterogeneity of deep mantle

1.通过高压实验、量热法和拉曼光谱晶格振动模拟，分别确定了MgAl_2O_4-Mg_2SiO_4、MgAl_2O_4-NaAlSiO_4和KAlSi_3O_8体系中铁酸钙、六方相和硬锰矿的高压稳定场.用<2.5>~ 1HAl-NMR<27>谱和X射线Rietveld分析研究了MgSiO_3-MgAlO_3体系钙钛矿中氧空位的形成。结果表明，在铝钙钛矿中存在两种离子取代（Mg^&lt;2+&gt;+Si^&lt;4+&gt; = 2Al^&lt;3+&gt;和2Si^&lt;4+&gt; + O^<2->= 2Al^&lt;3+&gt; +V^0）.详细测定了CaMgSi_2O_6、CaSiO_3和CaTiSiO_5-CaSi_2O_5系统的高压相关系。在SrSiO_3的相变研究中，我们发现了新的六方钙钛矿结构的SrSiO_3和新的巴格_2 O_5 Ⅲ型SrSi_2O<5->_4。测量了各种高压A^&lt;2+&gt;B^&lt;4+&gt;O_3钙钛矿的生成焓并确定了稳定性关系。我们发现了形成半径和阳离子半径之间的系统关系。这些关系式为估计未知钙钛矿的形成压力和合成压力提供了有益的指导.测量了Mg_2SiO_4改性尖晶石和尖晶石的标准熵，并用于计算橄榄石改性尖晶石-尖晶石转变和后尖晶石转变。结果表明，后尖晶石转变发生在660 km深度的压力下，温度约为1900 K，这证实了后尖晶石转变是造成660 km不连续的原因。CaIrO_3的后钙钛矿转变边界具有与MgSiO_3一致的强正P-T斜率。

1. High-pressure stability fields of calcium ferrite, hexagonal phase and hollandite were determined in the systems MgAl_2O_4-Mg_2SiO_4, MgAl_2O_4-NaAlSiO_4 and KAlSi_3O_8, respectively, based on high-pressure experiments, calorimetry, and lattice vibrational modeling using Raman spectra.2. Formation of oxygen vacancies in perovskites in the system MgSiO_3-MgAlO_<2.5> was established by studies using ^<27>Al-NMR spectroscopy and X-ray Rietveld analysis. We concluded that two types of ionic substitutions (Mg^<2+>+Si^<4+> = 2Al^<3+> and 2Si^<4+> + O^<2-> = 2Al^<3+> +V^0) occur in the aluminous perovskites.3. High-pressure phase relations in CaMgSi_2O_6, CaSiO_3 and in the system CaTiSiO_5-CaSi_2O_5 were determined in detail. In phase transition study on SrSiO_3, we found new hexagonal perovskite of SrSiO_3 and new BaGe_2O_5III-type SrSi_2O_<5->.4. Enthalpies of formation were measured and stability relations were determined for various high-pressure A^<2+>B^<4+>O_3 perovskites. We found systematic relations between the enthalpies of formation and cationic radii. The relations provide useful guide to estimate enthalpies of formation and synthesis pressures of unknown perovskites.5. Standard entropies of Mg_2SiO_4 modified spinel and spinel were measured, and used to calculate olivine-modified spinel-spinel transitions and postspinel transition. The results indicated that the postspinel transition occurs at pressure of 660 km depth at about 1900 K, which confirms that the postspinel transition is responsible for the 660 km-discontinuity.6. Post-perovskite transition boundary of CaIrO_3 has a strongly positive P-T slope, consistent with that of MgSiO_3.