应用XRD和HRTEM研究红粘土中的磁性矿物——以阿尔金新近系彩虹沟组剖面上段红粘土为例
魏小燕，李建星*，潘 峰，韩延兵，刘 三
（中国地质调查局西安地质调查中心，陕西 西安710054）
摘 要 前人已利用岩石磁学法对阿尔金彩虹沟组剖面上段红粘土的磁化率进行了研究，但对其中磁性矿物的种类和物相组合研究仍不足，因此，本文在前人研究的基础上，利用粉末X射线衍射和高分辨透射电镜对该红粘土中的磁性矿物进行物相鉴定和微观结构研究。结果表明，该红粘土中的磁性矿物基本为赤铁矿，这与前人用间接岩石磁学方法研究得出的结论一致。高分辨透射电镜观察下，具有风成形貌特征的赤铁矿为微米级-亚微米级颗粒，多数为大量纳米级赤铁矿组成的多晶集合体，少数载磁矿物颗粒具有磁赤铁矿核+赤铁矿边的组合关系，此外，大量纳米级赤铁矿多晶集合体的存在主要和干旱化事件有关。主要磁性矿物类型和显微结构研究为阿尔金风尘堆积红粘土形成于干旱化事件提供了矿物学证据。
关键词 红粘土；磁性矿物；赤铁矿；古气候
中图分类号： 文献标识码：A doi:10.3969/j.issn.1000-6281.2021.01.006
Study on the magnetic minerals in red clay by XRD and HRTEM using the red clay in the upper section of Neogene Caihonggou formation in Altun as an example
WEI Xiao-yan, LI Jian-xing*, PAN Feng, HAN Yan-bing, LIU San
(1. Xi’an Center of Geological Survey, China Geology Survey, Xi’an Shannxi 710054, China)
Abstract The magnetic susceptibility of red clay in the upper section of the Caihonggou formation in Altun has been studiedusing the rock magnetism method. However, there are still insufficient researches on the type and phase combination of magnetic minerals. Therefore, based on previous studies, X-Ray Powder Diffraction (XRD) and High Resolution Transmission Electron Microscopy (HRTEM) were used to study the phase combination and microstructure of magnetic minerals in this red clay. The results show that the magnetic mineral in the red clay is hematite, which is consistent with the conclusion obtained by previous studies using indirect rock magnetism method. Under the observation of HRTEM, the hematite with eolian morphology is micron-submicron particles. Most of them are polycrystalline aggregates composed of a large number of nanometer hematite. There is the mineral symbiosis relation between hematite nuclei and hematite edge in a few magnetic mineral particles. In addition, the existence of a large number of nanometer hematite polycrystalline aggregates is mainly related to the arid event. The study of magnetic mineral types and microstructure provides mineralogical evidence that Altun red clay was formed in the arid event.
Keywordsred clay; magnetic mineral; hematite; paleoclimate
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