Phase equilibrium study of mantle minerals at high pressure and high temperature.

作者用MA8装置发展了压力大于25 Gpa、温度高达2000ﾟC的高压和高温实验的基本技术。通过性能试验对不同的顶锤材料进行了评价，探索出了产生高压的最佳条件。此外，还对加热炉组件进行了改进，以达到更高的温度，并将热电偶故障降至最低。在高压和高温实验技术改进的基础上，对主要地幔矿物进行了如下相平衡研究：发现透辉石在18 Gpa以上的压力下分解为CaSiO_3钙钛矿和MgSiO_3组分的组合。在压力高达27 Gpa、温度1500ﾟC的条件下，精确测定了顽火辉石-镁橄榄石体系的相关系。此外，利用MA8和透射电子显微镜研究了镁橄榄石向脊状结构的转变机理。根据目前和最近测定的相平衡数据，估算了镁橄榄石和镁橄榄石组成的相变。进行了矿物物理测试，将与这些相变相关的地震速度和密度变化与地球物理观测结果进行了比较。结果表明，计算得到的地幔速度和密度分布与上地幔和过渡区的观测结果吻合较好。

The author has developed the basic techniques for high pressure and high temperature experiments for pressures above 25 GPa and temperatures up to 2000ﾟC using an MA8 apparatus. A performance test has been adopted to evaluate different anvil materials and optimum conditions for high pressure generation have been explored. Moreover, improvements in the furnace assembly has been made to reach higher temperatures and to keep thermocouple failure minimum. Further, a digital recording system equipped with a micro-computer has been introduced, which has made phase equilibria studies to be conducted in greater accuracy than before.On the basis of these technical improvements in high pressure and temperature experiments, phase equilibrium studies have been made for major mantle minerals as follows: Diopside was found to decompose into assemblages of CaSiO_3 Perovskite plus MgSiO_3 components at pressures greater than 18 GPa. Precise determination of the phase relations in the system enstatite-pyrope has been made at pressures up to 27 GPa and temperatures at 1500ﾟC. Further, transformation mechanism of forsterite to spinal structures has been studied on the basis of both MA8 and transmission electron microscope (TEM) techniques.Phase transformations in pyrolite and MORB compositions have been estimated according to the present and recently determined phase equilibrium data by the authors. A mineral physics test has been made, in which seismic velocity and density changes associated with these phase transformations in a pyrolite composition are compared with those derived from geophysical observations. The results show that the calculated velocity and density profiles for the pyrolite mantle agree quite well with the observed distributions throughout the upper mantle and the transitions region.