Insights from electron backscatter diffraction into the origin of fibrous calcite veins in organic-rich shale from lower Es3 to upper Es4, Jiyang Depression, China

摘要: Abstract The origin of fibrous calcite veins developed in organic-rich shales, has attracted great attentions. However the growth direction, formation temperature and stress state are still controversial. shale from lower Es3 to upper Es4 Jiyang Depression been analyzed with electron backscatter diffraction technology (EBSD), which can characterize microstructures orientation mineral crystals situ. On basis core observation microscopic identification petrological characteristics, longitudinal horizontal profiles were measured by EBSD. Crystallographic information on veins, obtained pattern quality mapping, phase diagrams, grain distribution maps, Euler graphs, misorientations pole figures, clarifies origins these veins. results show that belong sharp-rhombohedral space lattice structure trigonal system. Calcite have a preferred profile, while there is no obvious profile. profile misorientation cause interference colour extinction difference under orthogonal light. crystal characteristics both sides middle line different, indicating direction syntaxial. A shallow burial environment suggested for initial forming evidence morphology most shape sharp-rhombohedron, some hexagonal prism shape. average indicates grains inhomogeneous. concentration small higher than large grains, cracks interior or border formed three directional extrusion circumstances.