【摘要】 <正> 本文在新近陆续发表的几篇文章基础上,综合全部地质产状、岩化计算、光性测定及X射线粉末法与单晶分析结果,对安徽庐枞、浙江寿昌、桐庐及有关地区火山岩中碱长石的调制结构特征及其成因意义进行初步探讨。重点讨论分属扬子区与沿海区两大不同构造单元内火山岩中碱长石的出溶特征及地质成因问题。因此,凡涉及X射线单晶,透射电镜分析方法及调制结构衍射特征具体描述等已见于前文的诸细节,这里一般均从略。更多还原

【Abstract】 Using X-ray single-crysatl and powder methods, a study on modulated structure of alkaline feldspars from three volcanic basins:Tonglu basin and Shouchang basin in coastland, and Lujiang-Zongyang basin in Lower Yangtze area, is presented in this paper. The mechanism of exsolution and their difference of rocks among the basins are discussed. Some conclusions are put forward as following:1. According to the degree of exsoluted decomposition, thirty analysed alkaline feldspar samples are classified into five classes. The side band diffraction caused by density modulation indicates that the exsolution degree is lowest (mixed solution) .The transverse modulation of which the wave surface is parallel to(010)indicates that the exsolution is complete. From mixed solution to complete exsolution, the variation in order Is: density modulation, two phase coherent, Na-phase in twin and incoherent with monoclinic K-phase, K-phase transversely modulated in the direction parallel to (010) and incoherent with Na-phase, K-phase decomposes into a more potassium-rich phase transversely modulated in the direction parallel to (010) forming a complex combination which is polyohase and incoherent with another. The complex structure and their twins are various and diverse.2. The types of exsolution modulation have their special distribution pattern in general, alkaline feldspar from Lujiang-Zongyang and other volcanic basins in Lower Yangtze area is mostly of low exsolution or mixed solution, but that from Tonglu and Shouchang basins is mostly of complete exsolution. The former is called Lu-Zong type and the later Tong-Shou type. There are distinct differences in degree and mechanism of exsolution between the two types. This phenomena verifies the inference presented by Professor Bragg in recent years that the structure of feldspar and its nature have regional feature.3. The relation between the ordering path and degree of exsolution decomposition of alkaline feldspar in volcanic rocks from the regions is further discussed. It is believed that the difference of ordering path etween the two types of alkaline feldspar is caused by the difference of their exsolution degree, and the former is subordinated to the latter.The geological factors induced the difference of exsolution degree between the two types of alkaline feldspar are also discussed. Some preliminary views about genesis are put forward in this paper.更多还原