应用扫描电镜-能谱分析技术研究松辽盆地营城组致密砂岩中火山灰的微观特征

魏小燕,叶美芳,朱津蕊,张 慧

应用扫描电镜-能谱分析技术研究松辽盆地营城组致密砂岩中火山灰的微观特征

魏小燕,叶美芳,朱津蕊,张  慧

(1.中国地质调查局西安地质调查中心,陕西 西安710054;2.SGS通标标准技术服务有限公司,北京100176)

摘 要    利用场发射扫描电镜-能谱观测松辽盆地营城组致密砂岩时,发现一些不同于一般陆源碎屑的颗粒。详细的微观形貌和微区能谱分析结果表明,这些颗粒为火山灰,且以玻屑为主。低倍镜下,火山灰粒径以粉砂级为主,呈凹面棱角状、弧状或者长条状,排列无方向,与泥质紧密接触;颗粒表面平坦,干净,且常见贝壳状或平行线状断口。高倍镜下,火山灰由外及内脱玻化作用明显,呈港湾状边缘,内部可见微纳米气液包体孔。脱玻化后的矿物有微纳米级(0.5 ~ 5 μm)的石英和高岭石、绿泥石、伊利石等粘土矿物。能谱分析结果显示,火山灰的Si: O原子比通常为1: 1 ~ 4: 1不等,其比值普遍大于石英的Si、O原子比1: 2。这些微纳米现象的揭示与认识为识别细粒碎屑岩中的分散状火山灰提供了新的依据和途径。

关键词    营城组;致密砂岩;火山灰;微观特征;场发射扫描电镜-能谱

中图分类号:P572; P575.2; P577[A1]   文献标识码:A    doi:10.3969/j.issn.1000-6281.2022.02.007

 

Microscopic characteristics of volcanic materials in tight sandstone of Yingcheng Formation in Songliao Basin by SEM - EDS

WEI Xiao-Yan1,YE Mei-Fang1,ZHU Jin-Rui1,ZHANG Hui2

(1. Xi’an Center of Geological Survey, China Geology Survey, Xi’an Shaanxi 071005; 2. SGS Tongbiao Standard Technology Service Co., Ltd.,Beijing 100176, China)

Abstract  When the tight sandstone of Yingcheng Formation in Songliao Basin is observed by field emission scanning electron microscope - energy disperse spectroscopy (FESEM - EDS), some grains which are different from the common terrigenous debris are found. Detailed microtopography and energy spectrum analysis results show that these particles are volcanic ash, and mainly vitric pyroclast. At low magnification, volcanic ash is concave-angular, arc, stripped or blocky in shape, and has the same size as silts. The volcanic ash is arranged in no orientation and in close contact with the mud; particle surface is flat, clean, and many conchoidal or parallel linear fractures can be observed. At high magnification, the volcanic ash devitrification from outside to inside is obvious. The edge of the particle is harbor shaped, and the micro - nano gas - liquid inclusion pores can be seen inside. The minerals that have been deglazed are micro - nano (0.5 ~ 5 μm) quartz, clay minerals such as kaolinite, chlorite, illite and so on. Energy spectrum analysis shows that the Si: O atomic ratio of volcanic ash is usually 1: 1 - 4: 1, which is generally larger than that of quartz 1: 2. These phenomena in micro/nano scale provide a new basis and way for the identification of dispersed volcanic materials in fine - grained clastic rocks.

Keywords   Yingcheng formation; tight sandstone; volcanic ash; microscopic characteristics; FESEM - EDS

 

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