基于电子背散射衍射技术的纤维状方解石脉体晶体分析

Crystal characteristics of fibrous calcite veins based on Electron Back Scattered Diffraction (EBSD)

赵兰全 李志鹏 邹开真 马晓楠 刘振阳 尹鹤 雷利庆 禹宝军 马存飞

ZHAO Lanquan LI Zhipeng ZOU Kaizhen MA Xiaonan LIU Zhenyang YIN He LEI Liqing YU Baojun MA Cunfei

中国石化 胜利油田 勘探开发研究院, 山东 东营 257100 中国石油 青海油田 勘探开发研究院, 甘肃 敦煌 736200 中国石油 大港油田 采油五厂, 天津 300000 中国石油 新疆油田 勘探开发研究院, 新疆 克拉玛依 834000 布鲁克(北京)科技有限公司, 上海 201100 中国石油大学（华东）地球科学与技术学院, 山东 青岛 266580

Exploration and Development Research Institute of Shengli Oil Field, SINOPEC, Dongying, Shandong 257100, China Exploration and Development Research Institute of Qinghai Oil Field, CNPC, Dunhuang, Gansu 736200, China No.5 Oil Production Plant of Dagang Oil Field, CNPC, Tianjin 300000, China Research Institute of Exploration and Development, Xinjiang Oilfield Company, PetroChina, Karamay, Xinjiang 834000, China Bruker (Beijing) Scientific Technology Co., Ltd., Shanghai 201100, China School of Geosciences, China University of Petroleum (East China), Qingdao, Shandong 266580, China

方解石脉体广泛发育在富有机质页岩中，其岩石学特征和成因机制是研究的热点。电子背散射衍射技术能够原位表征矿物晶体的微观结构和晶体取向信息，而被广泛应用于材料科学领域，并在地质学领域得到了迅速发展。为了明确四川盆地龙马溪组富有机质页岩中纤维状方解石脉体的晶体特征，电子背散射衍射技术被用于表征方解石脉体的矿物学特征和结晶学特征。研究结果表明，方解石脉体的矿物组成为方解石和石英，其中方解石是主体，其晶粒的平均大小为372 μm；而石英主要分布在方解石纹层界面处。方解石脉体中的方解石晶体属于三方晶系或菱方晶系，相应的晶胞类型为三方晶胞或菱方晶胞，其晶格常数为a0=b0=4.99 Å，c0=17.061 Å，α=β=90°，γ=120°。方解石脉体在纵剖面上具有一定的择优取向，原因是方解石晶粒内部发育聚片双晶，其中相邻的双晶条纹具有不同的晶体取向，晶体取向差为75°；而相间的双晶条纹具有相同的晶体取向，且同一双晶条纹的晶体取向相同。方解石晶粒内部发育完全解理，常成组出现且与双晶条纹呈锐夹角斜交，两者均是在方解石结晶过程中受到构造压扭作用产生的，其中最大主应力方向与双晶条纹平行。

Calcite veins are widely developed in organic-rich shale, and their petrological characteristics and genetic mechanism are the focus of research. The Electron Back Scatter Diffraction (EBSD) can characterize the micro-structure and orientation of mineral crystals in situ, which has been widely used in the field of material science and has been rapidly developed in the field of geology. In order to clarify the crystal characte-ristics of fibrous calcite veins in organic-rich shale of the Longmaxi Formation in the Sichuan Basin, EBSD was used to characterize the mineralogical and crystallographic characteristics of calcite veins. The calcite veins are mainly composed of calcite and quartz. Calcite is the main body, with an average grain size of 372 μm, while quartz is mainly distributed at the interface of calcite lamina. The calcite crystals in calcite veins belong to trigonal[JP] or rhombohedral system, and the corresponding unit cell is trigonal or rhombohedral. The lattice parameters are a0=b0=4.99 Å, c0=17.061 Å, α=β=90°, γ=120°, respectively. Calcite veins have a certain preferred orientation on longitudinal section, which is due to the development of polysynthetic twin crystals in calcite grains. The adjacent twin crystal stripes have different crystal orientations, and the crystal misorientation is 75° while the alternate twin stripes have the same crystal orientation, and the crystal orientation of the same twin stripe is the same. In calcite grains, perfect cleavage occurs in groups with sharp angle with twin crystal stripes. Both cleavage and twin crystal stripes are formed by tectonic compression and shearing during the crystallization of calcite, and the maximum principal stress direction is parallel to the twin crystal stripes.

国家自然科学基金 41802172;国家自然科学基金 42172153;中央高校基本科研业务费专项 20CX02109A

https://doi.org/10.11781/sysydz202202357