岩石中斜长石双晶的背散射电子衍射测试与分析  

Electron Back-Scatter Diffraction Analysis for Twins of Plagioclase in Some Rocks

作　　者：赵珊茸[1] 刘宇坤 徐畅[1] Zhao Shanrong;Liu Yukun;Xu Chang(School of Earth Sciences,China University of Geosciences,Wuhan 430074,China)

机构地区：[1]中国地质大学地球科学学院,湖北武汉430074

出　　处：《地球科学》2022年第4期1399-1414,共16页Earth Science

基　　金：国家自然科学基金项目(No.41872037)。

摘　　要：斜长石双晶很常见,双晶律达10多种,但斜长石的各种双晶律在光学显微镜下不容易鉴别.基于背散射电子衍射(EBSD)技术,对产于大别山地区的3种岩石(花岗岩、闪长岩、变粒岩)中斜长石双晶进行了精确测定.3种岩石中均以卡-钠复合双晶(包括钠长石律、卡斯巴律、卡-钠复合律)为主,这种卡-钠复合双晶在光学显微镜下只表现为两个聚片单体的聚片双晶,还有1个或2个单体以晶畴形式分散在聚片单体中,在光学显微镜下不可辨别.除了卡-钠复合双晶外,偶见肖钠长石律、柱面{130}、{1-30}和{110}律.并发现了新的斜长石双晶律的复合关系和规则连生关系:(1)卡斯巴律-柱面{1-30}律-柱面{110}律可以形成复合双晶;(2)卡-钠复合律-柱面{130}律-柱面{1-30}律可以形成具三-六方对称的规则连生体,但不能形成复合双晶.基于本文有限的斜长石双晶统计数量,3种岩石中斜长石各双晶律出现的概率差异不大,可能斜长石双晶律出现概率与成岩条件关系不大.精确测定斜长石双晶律的方法,为今后大规模测量统计岩石中斜长石双晶律、发现新的斜长石双晶律及其复合关系等,提供一种方便有效的方法与手段.Twins in plagioclase are very common,and the twin laws are of more than 10 types.However,these twin laws are difficultly distinguished under optic microscope.In this paper,it provides a method based on electron back-scatter diffraction(EBSD)technique to determine accurately twin laws of plagioclase in three kinds of rocks(granite,diorite and leptite),occurring in Dabie Mountain,China.It is found that albite-carlsbad compound twin(including Albite law,Carlsbad law and Albite-Carlsbad law)is the most common twin type in the plagioclase in these three rocks.However,this Albite-Carlsbad compound twin(including 3-4 individuals)under EBSD test is just a polysynthetic twin(only 2 individuals)under optic microscope,because there are 1-2 individuals appearing as small domains inside other individuals,which cannot be resolved under optic microscope.A small amount of Pericline law,Prism{110},{130}and{1-30}laws are also found.A new compound twin among Carlsbad law,Prism{110}law and Prism{1-30}law is found.The Albite-Carlsbad law,Prism{130}law and Prism{1-30}law can co-exist together to form an intergrowth with three-six fold symmetry,but they cannot form a compound twin.Based on the limited amount of statistics in this paper,the probability of twin laws of plagioclase is unvaried among these three kinds of rocks,possibly reflecting that the twin laws of plagiocalse are not related closely to the formation condition of rocks.The method provided in this paper to analyze twin laws of plagioclase based on EBSD is effective and convenient,which will be helpful to statistic twin laws of plagioclase in rocks on a large scale,and find some new twin laws as well as new compound twins.

关 键 词：斜长石 双晶律 电子背散射衍射(EBSD) 极图 矿物学 

分 类 号：P572[天文地球—矿物学] P583[天文地球—地质学]