聚集型高演化天然固体沥青成因——以湘西脉状碳沥青为例

Formation Mechanism of Aggregated Type Natural Bitumen with High Evolution Degree: With Vein Anthraxolite in Xiangxi as an Instance

聚集型高变质程度的脉状碳沥青广泛存在于湖南湘西州寒武系地层,通过野外调查和实验测试,获得了碳沥青赋存特征、微观形态特征及母质来源、组成和演化程度等信息。野外调查发现,碳沥青矿脉大多赋存北东—北北东走向的小断裂内,通过扫描电镜及能谱(SEM-EDX)技术、X射线衍射光谱(XRD)技术、傅里叶红外光谱(FT-IR)技术测试了样品的微观形态、元素组成及分子结构。扫描电镜照片显示碳沥青具备流动状结构与镶嵌结构,X射线衍射光谱也有石墨的衍射峰出现,说明碳沥青达到了较高的演化阶段;红外光谱的官能团信息显示碳沥青源于干酪根的演化;通过实验数据的对比分析发现,无论是微观形貌还是组分特征,碳沥青既保留了原始石油的一些特征又受到强烈的后期改造影响,部分原始特征甚至被后期改造掩盖。

The metamorphic grade aggregated type natural vein anthraxolite is widespread in Cambrian strata in Xiangxi, Hunan. The characteristics of its occurrence and microscopic morphology, the source, the composition and the evolution degree are obtained based on the field investigation and analysis. Anthraxolite Veins are hosted mainly in the NE-NNE small faults. With the SEM-EDX （scanning electronic microscopy with energy dispersive X-ray）, the XRD techniques and the Fourier transform infrared spectrophotometer （FT-IR）, the chemical composition, the morphology and the molecular structure characteristics are identified. The data suggest that the anthraxolite is in a high evolution stage because of the flow structure and the mosaic texture of the SEM images and the graphite diffraction peak of XRD. The functional groups from the Fourier infrared absorption spectrometry illustrate the anthraxolite derived from the kerogen evolution. The anthraxolite with the characteristics of the original oil is shown, and it is influenced in the later stage, which sometimes even covers up the original features.