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High Pressure Phase Transformations Down to the Lower Mantle Conditions and Implications for the Nature of the Seismic Discontinuities.

下地幔条件下的高压相变及其对地震不连续性性质的影响。

基本信息

批准号：
07454105
负责人：
IRIFUNE Tetsuo
金额：
$ 4.93万
依托单位：
Ehime University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1997
项目状态：
已结题

项目摘要

High pressure and high temperature experiments have been made on mantle materials using both quench method and in situ X-ray diffraction measurement. The phase transformations in a pyrolite composition were studied by the former method at pressures to 28 GPa and temperatures along a representative mantle geotherm.It was demonstrated that iron partitioning of the coexisting phases in this composition affects significantly the width of the pressure interval between the modified spinel and spinel phases of olivine, which is consistent with the nature of the 410km discontinuity revealed by the recent seismological studies. On the other hand, we presented some data on the partitioning of iron between perovskite and magnesiowustite under the lower mantle conditions, and showed that the iron partition coefficient approaches unity with increasing pressure as a result of the increase of aluminum in the perovskite phase. The sharpness of the 660km seismic is discussed on the basis of these experimental data.The phase boundary between spinel and the postspinel phase has been determined by in situ X-ray measurements using a combination of the synchrotron source (SPring-8) and a multianvil device. The boundary was determined at temperatures up to about 2000ﾟC,demonstrating that the postspinel phase boundary has a negative Clapeyron slope as estimated by quench experiments and thermodynamic analyzes. The boundary was located at about 21 GPa, at 1600ﾟC,which is about 2GPa lower than the earlier estimations based on other high pressure studies.

采用淬火法和原位X射线衍射测量对地幔材料进行了高压和高温实验。采用前一种方法，在压力至 28 GPa 和沿典型地幔地温的温度下，研究了硫磺岩组合物中的相变。结果表明，该组合物中共存相的铁分配显着影响了橄榄石的变质尖晶石和尖晶石相之间的压力间隔宽度，这与最近地震学研究揭示的 410km 不连续性的性质是一致的。另一方面，我们提供了一些关于下地幔条件下铁在钙钛矿和镁方铁矿之间分配的数据，并表明由于钙钛矿相中铝的增加，铁分配系数随着压力的增加而接近一致。根据这些实验数据讨论了660km地震的锐度。使用同步加速器源（SPring-8）和多砧装置的组合，通过原位X射线测量确定了尖晶石和后尖晶石相位之间的相界。该边界在高达约 2000°C 的温度下确定，表明通过淬火实验和热力学分析估计后尖晶石相边界具有负克拉佩龙斜率。边界位于约 21 GPa，温度为 1600°C，比早期基于其他高压研究的估计低约 2 GPa。