Phase Transformations and Thermodynamic Properties of Constituent Minerals of Slabs in the Lower Mantle

下地幔板片组成矿物的相变和热力学性质

• 批准号: 11440162
• 负责人: AKAOGI Masaki
• 金额: $ 1.73万
• 依托单位: Gakushuin University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 1999
• 资助国家: 日本
• 起止时间: 1999 至 2001
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-11440162/
• 关键词: high-pressure transition; calorimetry; lower mantle; slab; perovskite; ilmenite; garnet; プロブスカイト; 玄武岩; 熱測定; カルシウムフェライト; メジャーライト; high-pressure transition; calorimetry; lower mantle; slab; perovskite; ilmenite; garnet; プロブスカイト; 玄武岩; 熱測定; カルシウムフェライト; メジャーライト

High-pressure phase relations of minerals consisting of MORE and pyrolite in slabs subducting into the lower mantle were investigated up to pressure-temperature conditions of the uppermost lower mantle. Calorimetric measurements were also performed, and phase relations were determined using the obtained thermodynamic data. Main results are as follows.(1) High-pressure phase relations in the systems MgAl_2O_4-NaAlSiO_4 and MgAl_2O_4-CaAl_2O_4 were clarified up to 30 Gpa, and a new phase with hexagonal symmetry was found. Structural analysis of the hexagonal phase showed that this phase has a new structure related to calcium-ferrite structure. This phase may be an important host of alkali elements and aluminum in the lower mantle. Phase transitions in NaAlSiO_4 were also examined by high-pressure experiments and calorimetry, and the phase boundary for transition to NaAlSiO_4 calcium ferrite was determined.(2) Phase relations in the system Mg_4Si_4O_<12>-Mg_3Al_2Si_3O_<12> were examined at 1000 ℃ up to 27 Gpa. It was clarified that garnet solid solution transforms to ilmenite solid solution which further transforms to perovskite solid solution. Enthalpies of the garnet-ilmenite-perovskite transitions were measured, and the phase boundaries were calculated. Based on the results, it was established that the garnct-ilmcnitc-pcrovskitc transitions occur in pyrolite in subducting slabs at the uppermost lower mantle.(3) Enthalpies of perovskite solid solutions in the systems CaSiO_3-CaTiO_3 and CaSiO_3-CaGeO_3 were measured, and the enthalpy was estimated for CaSiO_3 perovskite which cannot be recovered at ambient conditions. Phase relations of CaSiO_3 perovskite, one of major constituent minerals of the lower mantle, were thermodynamically calculated.

研究矿物质的高压相位关系，这些矿物质由更多的板和下套中的黄铜组成，直到最高地幔的压力温度条件为止。还进行了量热测量，并使用获得的热力学数据确定相位关系。主要结果如下。（1）系统中的高压相位关系MGAL_2O_4-NAALSIO_4和MGAL_2O_4-CAAL_2O_4我们最多澄清了30 GPA，并且发现了具有六边形对称性的新阶段。六边形相的结构分析表明，该相具有与钙 - 有限岩结构相关的新结构。该阶段可能是下层中碱元素和铝的重要主宿主。还通过高压实验和量热法检查了NaAlsio_4中的相位过渡，并确定了向Naalsio_4钙铁酸钙过渡的相边界。（2）在系统MG_4SI_4O_ <12> -MG_3AL_3AL_2SI_3O_3O_3O_3O_3O_3O_3O_3O_3O_3O_3O_3O_3O_2SI_3O_3O_3O_3O中检查了27 GPA。澄清说，石榴石固体溶液会转化为伊利特固体溶液，该溶液进一步转化为钙钛矿固体溶液。测量了石榴石 - 硅酸盐 - 栖息地的焓，并计算了相边界。基于结果，确定garnct-ilmcnitc-provskitc跃迁发生在黄金岩中，在俯冲下面的下层下地幔的平板中。在环境条件下恢复。 casio_3钙钛矿的相位关系，是下幔的主要组成矿物之一，是热力学计算的。