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报道了在400MPa,20～950℃条件下,二云母片麻岩弹性波速度的温度响应及时间对测量数据影响的实验结果.在600～800℃温度区间,弹性波速度快速降低,其原因至少与白云母的脱水和α-石英在相变为β-石英前弹性软化有关.而在875℃之上,Vp快速上升反映出石英进入了相对高速的β-相.在950℃,详细测量了弹性波速度与实验时间的关系.结果表明,在30h之内片麻岩的波速随时间的增加而迅速下降,下降幅度达到9.9%.与之对应的是弹性波的振幅也快速衰减,其幅度达到80%以上.其后波速和振幅趋于稳定.950℃时片麻岩弹性波波速和振幅随时间的变化反映出黑云母逐步脱水并最终趋于稳定的过程.实验结果为认识大陆地壳地震波速度反转现象提供了有益的启示.对于加厚的中-上地壳和高地温梯度环境(例如,青藏高原南部),石英的α-β相变不可避免,并且其相变前的弹性软化与白云母的脱水(脱水熔融)的温压区间重叠.因此,两者共同造成岩石弹性波速度的显著下降.在低速层之下,α-β石英相变有可能形成可被探测的高速薄层.高速薄层的识别可以为确定地温梯度提供了精确的约束条件.
The experimental results of temperature response and time of elastic wave velocity of mica gneiss at 400MPa and 20-950 ℃ are reported.The elastic wave velocity decreases rapidly at 600-800 ℃ for at least the reason Is related to the dehydration of muscovite and the softening of α-quartz before the transformation to β-quartz, while the rapid rise of Vp above 875 ° C reflects the quartz entering the relatively high-speed β-phase. At 950 ° C, Elastic wave velocity and experimental time.The results show that within 30h, the velocity of gneiss decreases rapidly with the decrease of 9.9%, which corresponds to the fact that the amplitude of elastic wave decays rapidly and its amplitude Reaching more than 80% .After that, the wave velocity and amplitude tended to be stable.The variation of the wave velocity and amplitude of gneiss at 950 ℃ showed that the biotite gradually dewatered and finally tended to be stable.Experimental results In order to understand the continental crust seismic wave The inversion of velocity provides useful enlightenment.The α-β phase transformation of quartz is unavoidable for the thickened mid-upper crust and the high-temperature gradient environment (eg, the southern part of the Qinghai-Tibet Plateau), and its elastic softening before transformation muscovite Of the dehydration (dehydration melting) of the temperature and pressure overlap, so both together cause a significant decline in rock elastic wave velocity below the low-speed layer, α-β quartz phase transition may form a high-speed thin layer can be detected. The identification of thin layers can provide accurate constraints for determining the geothermal gradient.