【作者】 刘巍；

【导师】 杜建国；

【作者基本信息】 中国地震局地质研究所 ， 固体地球物理学， 2002， 博士

【摘要】 高温高压下岩石的弹性性质研究是探索地球内部奥秘的一个重要手段。尽管人们对弹性波速度(纵波速度和横波速度)的实验研究比较多，但实验的压力和温度条件(目前大多低于1.0GPa和900℃)还有待提高。在弹性波动力学特征如波形、振幅、频率及衰减等方面研究薄弱。因此，有必要在更高的温压条件下对弹性波通过壳幔岩石的速度和动力学特征等方面进行深入研究。 在总结高温高压条件下岩石弹性波速度和动力学特征研究进展的基础上，运用超声波脉冲透射法、透射—反射联用法和频谱振幅比法研究了几种壳幔常见岩石(斜长角闪岩、闪长岩、橄榄岩、辉石岩、蛇纹石化辉石岩和蛇纹岩)的弹性纵波速度和纵波首达波的振幅、总能量、频谱和衰减等动力学特征随压力(0.4～4.0GPa)和温度(室温～1240℃)的变化特征。在1.0GPa压力下、不同温度处获得了多个不同样品的实验产物。利用光学显微镜和电子探针分析了实验产物的矿物成分和结构的变化特征，并据此分析了导致弹性纵波速度和动力学特征变化的原因。实验结果为了解地球内部物质之间的相互作用，为研究岩石圈的精细结构和演化过程和解释低速层的产生、深部震源物质的演化以及地震前兆等各种地质过程提供了新的科学依据。 在0.4～4.0GPa压力范围内，岩石的纵波速度随压力增加而增大，高压时波速的增大幅度小于低压时波速的增大幅度。这主要是由于低压时纵横比低的孔隙易于闭合，随着压力增加，大量纵横比低的孔隙均已闭合，岩石表现出接近于组成岩石样品的全部矿物自身固有的弹性性质，因此高压时波速增大的幅度减小。当压力升高时，弹性纵波通过橄榄岩和辉石岩的首达波的波峰和波谷的绝对值、能量和品质因子值随之增大。原因是，在压力作用下，岩石的孔隙度降低，岩石内大部分裂纹闭合，并且矿物颗粒边界接触紧密，在裂纹表面和颗粒边界的能量损失减少。随压力升高，弹性纵波通过斜长角闪岩的首达波的波谷绝对值和品质因子值增大，但波峰略趋降低，能量和谱峰值均先增大后转为下降，这可能是由于斜长角闪岩在加压的过程中发生碎裂有关。弹性纵波通过三种岩石的首波的主频“漂移”现象不明显。 恒定压力下，橄榄岩和辉石岩的纵波速度随温度(室温～约1240℃)的升高呈线性下降；斜长角闪岩和闪长岩在室温至约600或800℃呈线性下降，当温度更高时，波速迅速降低；蛇纹石化辉石岩纵波速度在低温时(室温～500℃)随温度升高呈线性降低，当温度继续升高，波速出现了迅速降低，继而快速增大，后又急剧下降的变化特征。低温时，岩石内部矿物热膨胀导致纵波速度随温度呈线性缓慢下降；高温时，脱水作用、部分熔融以及生成反应边等导致波速随温度升高呈快速非线性降低。在1.0-3.0GPa实验压力范围内，弹性纵波通过橄榄岩、辉石岩和斜长角闪岩的首波的波峰和波谷的绝对值、能量、谱峰值和品质因子值随温度的升高而降低，其中斜长角闪岩在高温时(＞1100℃)纵波首波的波峰和波谷很低，几乎趋于零，品质因子值在约900℃时大幅度降低。这主要归因于高温下晶体内的缺陷增多和由于颗粒边界空位较多、晶格滑动或颗粒边界位错导致的颗粒边界阻尼效应以及流体自身的非弹性。弹性纵波通过橄榄岩、辉石岩和斜长角闪岩的首波的主频随温度升高呈先增大后减小的变化趋势。 将弹性波速度和弹性波动力学高温高压实验结果与地球物理探测资料联合起来进行反演，则能够建立更为合理的岩石圈结构。闪长岩、斜长角闪岩和蛇纹石化辉石岩的脱水和部分熔融可用于解释地壳和上地慢上部的低速层或低速高衰减层。含水矿物脱出的水发生逸散可能是高速层形成的原因。高温高压实验中岩石脱水和熔融对弹性波速度和动力学性质的影响与地震中监测到的波速异常和动力学特征变化类似，因此岩石弹性波性质的高温高压实验结果为地震孕育(特别是化学过程直接或间接致震)和地震预报的研究提供了参考依据和实验基础。更多还原

【Abstract】 The study on the elastic property of rocks at high pressures and high temperatures (HPT) plays an important role in researching the earth interior. Though there has been much progress in the measurement of elastic wave velocity, the experimental pressures and temperatures are still not high enough(<1.0GPa, <900℃). The knowledge about the elastic wave dynamic characteristics such as waveform, amplitude, frequency and attenuation (Qp, quality value) is very limited. Therefore, the elastic wave velocity and dynamics on crustal and mantle rocks at much higher PT should be further studied.The development of the study on the elastic wave velocity and dynamics at HPT is reviewed. The compressional wave velocity(Vp) and dynamic characteristics including amplitude, energy, frequency and attenuation in some crust and mantle rocks(amphibolite, diorite, dunite, pyroxenite, serpentinized pyroxenite and serpentinite) are studied by means of the ultrasonic pulse transmission method, the ultrasonic pulse and echo-impulse method, and the spectral ratio method at the pressure from 0.4GPa to 4.0GPa up to 1240℃ in the laboratory. Some experimental products of different samples are obtained at the constant pressure of 1.0GPa and different key temperatures. The changes of the mineral and chemical contents and the fabric in the product interior are carefully observed under an optical microscope and with an electron microprobe analyzer. The reason of changes of the elastic P-wave velocity and dynamics is discussed in detail by combination of their experimental results and the p roduct i nterior c hanges. Thee xperimental r esults p rovide n ot o nly strong theory basis for understanding the interaction of the earth deep materials and studying the structure and evolution of the lithosphere, but also scientific evidence for researching the formation of low velocity zones, the evolution of the rocks in earthquake source regions, and earthquake precursors.Vp in samples increases with the pressure increasing, and shows a greater rising rate at the low pressure about 0.4-2.0GPa than that at about 2.0-4.0GPa. At the lower pressures, the pores with low aspect ratio in rocks are easy to close, and almost all of them would close with the pressure increasing. As a result, the samples show the internal inherent elasticity of the whole constituent minerals themselves and the increasing rate of Vp turns lower at the higher pressures. As the pressure rises, the absolute values of the wave crest and trough, energy and quality value of the first arriving P-waveform passing through the dunite and the pyroxenite increase, because the energy loss between the surfaces of cracks and the mineral boundaries is reduced due to the porosity decreasing and the mineral boundaries contact more tightly at higher pressures. Though the absolute value of the wave trough and QP of the first arriving P-waveform passing through the amphibolite increase, the wave crest appreciably decreases and the energy and the amplitude maximum first increase then decrease, which is possibly due to the amphibolite crashing during the loading. The main frequency (fm) drift of the first arriving P-waveform passing through the dunite,pyroxenite and amphibolite is not evident.At the constant pressure, the Vp in different rocks varies differently as the temperature increasing: the Vp of the dunite and the pyroxenite decreases linearly with the temperature increasing up to about 1240℃; the Vp of the amphibolite and the diorite decreases linearly from room temperature to 600℃ or 800℃, then rapidly drops at higher temperatures; the Vp in the serpentinized pyroxenite shows a linear decrease from room temperature to about 500℃, then an abrupt decrease, a rapid lift and again a remarkable drop as the temperature increasing. Commonly, the thermal expansion of rocks and minerals results in the linear reduction of Vp in rocks at lower temperatures, while at higher temperatures the dehydration, partial-melting, and reaction rims give rise to a sharp drop of the Vp. However, the Vp incre更多还原