长石中G.P.区的发现和确认

The Discovery and Confirmation of Guinier-Preston Zone in Feldspar

对产自江西乐安相山碎斑熔岩中的隐纹长石斑晶 (Or71 .5Ab2 7.6An0 .9)进行了透射电镜研究 ,揭示出其中不仅存在钠长石出溶叶片 ,且还有许多细小的碟形沉淀物 ,这两者均平行于主晶低透长石的 (6 0 1)分布 ,与主晶共格连生 .此种碟形沉淀物小片的宽度和长度分别介于 3～ 17nm和 2 0～ 36 0nm之间 ,均远小于钠长石叶片的尺寸 .它们呈丛聚状均匀地分布于各钠长石叶片之间的中央带内 ,而在中央带两侧毗邻钠长石叶片的边缘带内则无沉淀物出现 .此外 ,在沉淀物小片两旁可见一边白一边黑的基体应变场衬度 .在化学组成上 ,此细小沉淀物的Na含量高于透长石主晶而低于钠长石叶片 .根据以上特征 ,足以确认这些细小的碟形沉淀物小片乃是长石中的一种新的准稳定相———G .P .

Transmission electron microscopy study is carried out for a perthite phenocryst (Or 71.5 Ab 27.6 An 0.9)in the porphyclastic lava from Xingshan, Lean County, Jiangxi Province, China. It reveales that there are not only albite exsolution lamellae, but also lots of fine disc-shaped precipitates in this perthite. Both of them are parallel to (601) of low-sanidine host. The dimensions of these platelets range in 3～17nm in width and 20～360nm in length, and all of them are much smaller than albite lamellae. They are clusteredly and homogeneously distributed over the middle belts between albite lamellae, and the precipitate-free zones occur on both sides of the belts, and extend up to boundaries of lamellae. In addition, the matrix strain-field constrast can be seen as a bright area on one side of the precipitate platelet and a dark area on the other side. Chemically, the fine precipitate is richer in sodium than in sanidine host and poorer than in albite exsolution lamella. On the basis of the above-mentioned characteristics, it can be concluded that the precipitate platelets occurring in the studied perthite are the G.P. zones (Guinier-Preston zones).