A first-principles calculation of the elastic and vibrational anomalies of lizardite under pressure
A first-principles calculation of the elastic and vibrational anomalies of lizardite under pressure
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DOI：
10.2138/am.2013.4369
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发表时间：
2013-11
影响因子：
3.1
通讯作者：
J. Tsuchiya
中科院分区：
文献类型：
--
作者：
J. Tsuchiya
摘要利蛇纹石是三种蛇纹石矿物之一，对了解俯冲带的地质过程具有重要意义，俯冲带是蛇纹化的海底再循环进入地幔的地方。利用第一性原理技术研究了压力下利蛇纹石的晶体结构、弹性和振动性质。在10 GPa以上，得到了稳定和亚稳定的结构。稳定结构的氢键几何形状表明氢键在10 GPa以上消失，而亚稳结构在整个压力范围内直至20 GPa没有显示出任何明显的氢键强度变化。在10 GPa，一个非常突然的软化的弹性常数被观察到的稳定结构，这是与c轴的可压缩性的轻微变化。这种弹性软化导致地震波速度vP和vφ分别突然降低约16%和24%。然后，这些速度随着进一步压缩而急剧增加。另一方面，剪切速度vS随着压力逐渐减小，然后在10 GPa时突然增加约14%。OH伸缩振动频率在-10GPa处也突然增加。先前的拉曼测量报告，最高OH伸缩频率也急剧增加超过6 GPa。因此，有可能在大约6 GPa的压力下通过实验观察到这种弹性异常。
Abstract Lizardite, being one of three serpentine minerals is of considerable interest in connection with understanding the geological processes occurring at subduction zones where serpentinized ocean floor is recycled into the Earth’s mantle. The crystal structure, elasticity, and vibrational properties of lizardite under pressure were determined using first-principles techniques. Above 10 GPa, a stable and a metastable structures were obtained. The hydrogen bond geometry of the stable structure indicates the disappearance of hydrogen bonds above 10 GPa, whereas the metastable structure does not show any noticeable change of the hydrogen bond strength throughout the pressure range up to 20 GPa. At 10 GPa, a very sudden softening of the elastic constants was observed for the stable structure, which is associated with a slight change in the compressibility of the c axis. This elastic softening causes a sudden reduction in the seismic velocities vP and vφ by about 16 and 24%, respectively. These velocities then steeply increase with further compression. Shear velocity vS, on the other hand, gradually decreases with pressure and then abruptly increases about 14% at 10 GPa. The calculated OH stretching frequencies also increase suddenly at -10 GPa. Previous Raman measurement reported that the highest OH stretching frequencies also increase steeply above 6 GPa. Therefore, there is a possibility that this elastic anomaly can be observed experimentally at about 6 GPa.