Study on Microstructures of Granite by SEM Secondary-Electron, Cathodoluminescence, and Backscattered-Electron Images

用扫描电子显微镜(SEM)和光学显微镜观察了定向花岗岩样品的微观结构。EM可以清晰地获得三种图像：在给定样品的同一位置上的二次、背向散射电子和阴极发光图像。分别采集了日本西南部晚白垩世至古近纪早期分布在大型断裂周围和不含大型断裂的花岗岩类岩体，(1)Atera、Byobusan和Enasan断裂周围分布的Naegi-Agematsu花岗岩，(2)Asuke-cho、东Kamo-Gun、岐阜县稻川花岗岩周围，以及日本内海北岛岛、大岛岛的广岛花岗岩和圣城附近的广岛花岗岩。根据这些微结构的大小和位置，可以将它们分为三种变形微观结构(…较多的环状结构类型：晶间型是连续穿过多个晶体，晶界型存在于相邻晶体之间的接触处，晶内型存在于晶体中，不延伸到相邻晶体。晶间类型包括微角砾岩、愈合带、充填矿物裂隙和晶间裂隙。晶界类型强烈地依赖于相邻两个颗粒的矿物学。这种类型具有愈合的、充填矿物的锯齿状晶界、晶界裂缝和没药石。晶内型的出现与晶体的种类有关。石英中常见的是愈合裂纹和甲壳裂纹，而长石中则普遍存在微断层、解理裂纹、扭结带和机械孪晶。在两种矿物中都发现了波状消光和晶内裂缝。黑云母包括裂隙带、阶梯带、弯曲带、鱼带和扭结带。由于通过扫描电子显微镜背散射电子图像的对比可以清楚地认识到矿物学上的差异，这些图像有利于晶界微结构的形成。扫描电子显微镜阴极发光图像清晰地显示出石英中的带状结构，以及莫来石和锯齿状边界带的显微结构，这是光学显微镜无法观察到的。较少

Microstructures of oriented granitic samples were observed by a scanning electron microscope (SEM) and an optical microscope. Three kinds of images : secondary-, and backscattered-electron and cathodoluminescence images on the same position in a given sample, were able to be clearly obtained by the EM. The sampels were collected from Late Gretaceous to Early Paleogene granitic rock bodies distributed around large-scale faults or including no large-scale faults in Southwest Japan, respectively, (1) Naegi-Agematsu granite distributed around the Atera, Byobusan and Enasan faults, (2) Inagawa granite around Asuke-cho, East Kamo-Gun, Gifu Prefecture, and Hiroshima granite in Kitakijima and Oshima Islands in the Inland Sea of Japan and around Hagi City in San'in Region.The SEM and optical-microscope observations revealed that various types of microstructures existed in the granitic samples. Based on a scale and position of these microstructures, they are classified into three deformation mic … More rostructure types: intergranular type being continuous through multiple crystals, grain boundary type found at contacts between adjacent crystals, and intragranular type existing in a crystal with no extension to the adjacent crystals. The intergranular type includes microbreccia, healed zone, mineral-filled fracture, and intergranular crack. The grain boundary type strongly depends upon the mineralogy of the two adjacent grains. This type has healed, mineral-filled and serrated grain boundaries, grain boundary crack and myrmekite. Occurrence of the intragranular type is related to the kind of the crystals. Healed and carapace cracks are common in quartz, while microfault, cleavage crack, kink bands and mechanical twin commonly exist in feldspars. Undulatory extinction and intragranular cracks are found in both minerals. Biotite includes clevage crack and step, bend, fish and kink bands. Since differences in mineralogy are clearly recognized by contrast in SEM backscattered electron images, these images are good for grain boundary microstructures. SEM cathodoluminescense images clearly display banded structures in quartz and microstructures in myrmekitic and serrated boundary zones, which are impossible to be observed by the optical microscopy. Less