我国境内喜马拉雅地区第三纪花岗岩类中的长石成分和结构状态研究

在雅鲁藏布江-噶尔河一线以南,中印、中不、中锡和中尼边境以北的我国境内喜马拉雅地区,广泛出露着第三纪花岗岩类。它们以中-小型的岩体为主,零星断续地大致沿着喜马拉雅山系的总走向分布,构成一条范围广阔延伸千余公里的喜马拉雅第三纪花岗岩带。根据岩体的地质特征和岩石类型又可将该岩带分为二个带:高喜马拉雅电气石白云母花岗岩带和藏南低分水岭片麻状二云母花岗岩带。

STUDY ON THE COMPOSITION AND STRUCTURE OF FELDSPARS IN TERTIARY GRANITES OF HIMALAYAS AREA, CHINA

Small Tertiary granite bodies are distributed extensively in the Himalayas area. According to their geological features and lithologie types two belts can be distinguished: (1) High Himalayan tourmaline-muscovite granite belt, i:e. south belt, and (2) South Xizang Lower Ridge dimicaceous gneissic granite belt, i.e. north belt. The former can be further subdivided into two parts - the stocks and veins. The composition and structure of the feldspars obtained from ten granite bodies were determined by various methods, e.g. optical, X-ray and infra-red absorption and so on.Basing upon these determinations the following conclusions may be drawn: 1. The K-feldspars in the bodies are essentially intermediate microcline or "tric-linic orthoclase", but not simply orthoclases; 2. The ordering of the plagioclase is always higher than that of the K-feldspars in the same body; 3. Owing to the presence of volatile component in large amount the ordering and triclinicity of K-feldspars in the stocks of the south belt are more significant than that in the stocks of the north belt; 4. As veins cool down more rapid by cooling than stocks, the ordering and triclinicity of K-feldspars in the stocks are also more significant than that of K-feldspars in the veins from the same belt; 5. The composition of plagioclases in the same granite body varies in a more narrow range with a normal frequency curves. In short, it is suggested that the structure of feldspars in granites does not only depend on the geological age of the formation of the granite body, but also on the thermal history and the concentration of the volatiles.