不同种类岩石的太赫兹光谱特征研究

准确认识不同种类的岩石特征对地质构造、结构与年代的判断至关重要。常规光学显微手段虽然可以对岩石的颜色与表面形貌进行直接观测，但是对岩石种类的判断往往凭靠经验，一些颜色相近的矿物容易混淆，所得结果并不准确。光谱方法能够在不同频段给出样品的多个光学参数信息，通过建立光学参数与样品自身物性的联系，可以从多个维度确定样品的性质，从而有望实现对不同矿物成分与含量定性、定量评价。太赫兹光谱具备一定的穿透能力，能够透过一定厚度的岩石，是研究岩石物理性质的合理手段。基于太赫兹光谱技术，对取自不同地区的花岗岩、灰岩、砂岩和油页岩样品进行测试，分别计算得到每个样品的等效折射率n、衰减系数a，并以a为横坐标、n为纵坐标作图，结果表明，相同岩性岩石的n与a基本呈线性相关关系，而对于不同类型的岩石，其n随a的线性变化趋势存在明显区别。进而研究了岩石中的组成、结构等信息与其太赫兹光谱响应的联系，分析了不同岩性岩石的光谱响应机制，结果表明：花岗岩与灰岩的结构较为致密，其矿物组成是影响太赫兹光谱响应的主要因素，利用太赫兹参数能够估算岩石中铁、镁元素的相对含量；砂岩的成分较为单一，太赫兹光谱响应受孔隙度的影响；而对于油页岩来说，由于有机质具有强吸收、低折射率的特点，其有机质含量越高，折射率越低，对太赫兹吸收越强。结果表明，太赫兹光谱技术有望成为岩石物理性质现有研究手段的合理补充，为其评价、分析提供新技术、新指标，有着极其光明的应用前景。

Terahertz Spectral Characteristics of Rocks With Different L ithologies

Determining the types of rock is crucial to understand the origin and history of geological units.The recognition and classification of lithologies are usually performed by experienced researchers based on the colors and morphologies with the accuracy not guaranteed,particularly when trying to distinguish between units with similar lithology.Different from the subjective judgment,spectral means can provide multiple optical parameters among different frequencies.Information of the samples can be determined by establishing the relationship between optical parameters and the physical properties,to achieve qualitative and quantitative evaluation.In this study,terahertz(THz)spectroscopy was employed to discriminate the lithology of rock gathered from different regions.Based on the relations between effective refractive index(n)and attenuation coefficient(a),the samples can be classified into four gatherings,with the result in agreement with their lithologies.Besides,the variation tendency of THz parameters was plotted with the componential and structural properties,indicating that the variant THz responses were resulted by varying compositions and structures for different classifications of rocks.The mineral composition is the main factor affecting the absorption and refraction of the THz wave.Element content can be estimated with the THz parameters for Fe and Mg.For sandstone with stable elements,both the absorption and refraction of THz wave are negatively correlated with the porosity.Organic content in oil shale has a reverse effect on THz absorption and refraction,in which the higher oil yield results in a stronger absorption and lower refraction.Herein,the refractive index is positively correlated with the absorption for granite,limestone and sandstone,while the relation between them is negatively correlated for oil shale.Our results prove that the THz technique is a promising means for determining the lithology and petrophysics properties,which will be a significant supplementary in geology research.