Abstract

The results of measuring the frequency dependences of the attenuation coefficient and phase velocity of longitudinal ultrasonic waves in metasandstone samples with varying degrees of deformation–metamorphic alteration are presented to study the influence of the sample structure on these acoustic characteristics. The measurements are performed using broadband acoustic spectroscopy with a laser source of ultrasound and piezoelectric detection of nanosecond ultrasonic pulses in the 1–70 MHz operating frequency range. The metasandstones of the zonally metamorphosed Ladoga Group of the Paleoproterozoic Baltic Shield are studied, which exhibit varying degrees of structural and textural changes that occurred in the temperature range of 400–600°С. Cores of two different thicknesses with a similar mineral phase composition, but with some variations in the structural and textural composition of the substrate, were selected at four sampling points of different temperature levels and studied. For metasandstones from three sampling points, the frequency dependences of the attenuation coefficient and phase velocity of longitudinal ultrasonic waves almost completely coincide in three zones of each core and are nearly the same for cores of two different thicknesses. The latter fact confirms the reliability of the results of the ultrasonic studies, and the coincidence of the results for three different zones of each core shows that the structure of these metasandstones is uniform. The attenuation coefficient and phase velocity of ultrasound considerably differ in the studied zones of two metasandstone cores in one of the four sampling points (LV1246) due to the significant nonuniformity of their structure. In addition, for metasandstones from different sampling points, a difference in the absolute values of the attenuation coefficient and phase velocity of ultrasound is found in the entire studied frequency range. The Rayleigh model of ultrasonic scattering is used to estimate the maximum grain sizes in the studied samples. The results correlate with data obtained using optical microscopy of thin sections of all samples. The implemented broadband acoustic spectroscopy method with a laser source of ultrasound can help to reveal the relationship between the frequency dependences of the attenuation coefficient and phase velocity of longitudinal ultrasonic waves, the characteristic features of the structure, and conditions for the formation of metasandstones in each specific deposit.

中文翻译：

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超声激光源宽带声谱研究变砂岩的结构

摘要

提出了在不同变形-变质蚀变程度的变砂岩样品中测量纵向超声波的衰减系数和相速度的频率依赖性的结果，以研究样品结构对这些声学特性的影响。测量是使用宽带声波谱、超声波激光源和 1-70 MHz 工作频率范围内纳秒超声波脉冲的压电检测来进行的。对古元古代波罗的海地盾带状变质拉多加群的变砂岩进行了研究，这些变砂岩在 400–600°С 的温度范围内表现出不同程度的结构和质地变化。在不同温度水平的四个采样点选择两种不同厚度的岩心并进行研究，它们具有相似的矿物相组成，但基材的结构和质地组成有所不同。对于来自三个采样点的变砂岩，纵向超声波的衰减系数和相速度的频率依赖性在每个岩心的三个区域中几乎完全一致，并且对于两种不同厚度的岩心几乎相同。后一个事实证实了超声波研究结果的可靠性，并且每个岩心的三个不同区域的结果的一致性表明这些变砂岩的结构是均匀的。由于结构的显着不均匀性，四个采样点之一（LV1246）的两个变砂岩岩心的研究区域中超声的衰减系数和相速度存在显着差异。此外，对于不同采样点的变砂岩，在整个研究频率范围内，超声的衰减系数和相速度的绝对值存在差异。超声波散射的瑞利模型用于估计所研究样品中的最大晶粒尺寸。结果与使用所有样品的薄片的光学显微镜获得的数据相关。采用超声激光源实施的宽带声谱方法有助于揭示纵向超声波的衰减系数和相速度的频率依赖性之间的关系、结构的特征以及每个区域中变砂岩的形成条件。特定存款。