Electron Back-Scatter Diffraction Analysis for Twins of Plagioclase in Some Rocks
-
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}、{130}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{130}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{130}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.
-
关键词:
- 斜长石 /
- 双晶律 /
- 电子背散射衍射(EBSD) /
- 极图 /
- 矿物学
Abstract: 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 {130} laws are also found. A new compound twin among Carlsbad law, Prism{110} law and Prism{130} law is found. The Albite-Carlsbad law, Prism {130} law and Prism {130} 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.-
Key words:
- plagioclase /
- twin law /
- electron back-scatter diffraction /
- pole figure /
- mineralogy
-
表 1 斜长石晶体化学式
Table 1. The chemical formula of plagioclase
样品编号 晶体化学式(O=8.000) 长石端元组分 DT-37 (Na0.757Ca0.212K0.035Mg0.001Mn0.001Fe0.007)1.013
[(Al1.130Si2.845)3.975O8.000]Ab75.4An21.1Or3.5
更长石DT-24 (Na0.838Ca0.155K0.018Mn0.001Fe0.003)1.015
[(Al1.145Si2.847)3.992O8.000]Ab82.9An15.3Or1.8
更长石HA-17 (Na1.003Ca0.013K0.005Fe0.001)1.022
[(Al0.950Si3.028)3.978O8.000]Ab98.2An1.3Or0.5
钠长石表 2 斜长石与钾长石的晶胞参数测试结果
Table 2. The cell parameters of plagioclase and K-feldspar
样品编号 晶胞参数 a(Å) b(Å) c(Å) α(°) β(°) γ(°) DT-37 Pl 8.111 12.734 7.123 94.292 116.665 87.527 Kf 8.511 12.912 7.171 90.306 116.015 88.977 DT-24 Pl 8.150 12.838 7.160 94.570 116.675 87.774 Kf 8.580 12.923 7.196 89.922 116.250 89.240 HA-17 Pl 8.139 12.771 7.156 94.094 116.681 87.689 Kf 8.600 12.962 7.224 90.739 115.952 87.744 注:Pl. 斜长石;Kf. 钾长石. 表 3 斜长石双晶律的极图特征
Table 3. The pole figure characteristics of twin laws of plagiclase
双晶律种类 极图特征 钠长石律 {010}面, < 100 > 、 < 001 > 轴两单体极点重合;{100}、{001}面, < 010 > 轴两单体极点近于重合.特征概括为:3个主面和主轴都重合或近于重合 卡斯巴律 {100}、{010}、{110}、{130}面、 < 001 > 轴两单体极点重合; < 010 > 轴两单体极点近于重合.特征概括为:主轴 < 100 > 不重合,主面{001}不重合,但{hk0}面重合 卡-钠复合律 {010}面, < 001 > 轴两单体极点重合;{100}面, < 010 > 轴两单体极点近于重合.特征概括为:主轴 < 100 > 不重合,主面{001}不重合,且{hk0}面也不重合 肖钠长石律 {100}、{001}面, < 010 > 轴两单体极点重合;{010}面, < 100 > 、 < 001 > 轴两单体极点近于重合;简单概括为:3个主面和主轴都重合或近于重合.这与钠长石是相似的,与钠长石律区别是: < 001 > 轴两单体之间夹角为6.98°,这个角度在极图上也很难看出来.肖钠长石律与钠长石律只能通过双晶接合面的方向区别:钠长石律接合面为{010},肖钠长石律接合面为{h0l} 巴温诺律 {021}、{0$ \overline{2} $1}面, < 100 > 轴两单体极点重合,其他方向晶面或晶轴的极点关于{021}面对称 曼尼巴律 {001}面, < 010 > 、 < 100 > 轴两单体极点重合,{010}面两单体极点近于重合,其他方向晶面或晶轴的极点关于{001}面对称 柱面{110}律 {110}、{1$ \overline{3} $0}面, < 001 > 轴两单体极点重合,其他方向晶面或晶轴的极点关于{110}面对称 柱面{1$ \overline{1} $0}律 {1$ \overline{1} $0}、{130}面, < 001 > 轴两单体极点重合,其他方向晶面或晶轴的极点关于{1$ \overline{1} $0}面对称 柱面{130}律 {130}、{1$ \overline{1} $0}面, < 001 > 轴两单体极点重合,其他方向晶面或晶轴的极点关于{130}面对称 柱面{1$ \overline{3} $0}律 {1$ \overline{3} $0}、{110}面, < 001 > 轴两单体极点重合,其他方向晶面或晶轴的极点关于{1$ \overline{3} $0}面对称 阿拉律 < 100 > 轴,{010}、{001}面两单体极点重合; < 010 > 轴两单体极点近于重合,其他方向晶面或晶轴的极点关于垂直 < 100 > 的面对称 X律 {100}面, < 010 > 、 < 001 > 轴两单体极点重合;{010}面两单体极点近于重合,其他方向晶面或晶轴的极点关于{100}面对称 注:表格据 Xu et al., 2016 , 本文作者重新整理.表 4 二长花岗岩(DT-37)中斜长石双晶测试分析统计
Table 4. Twin analysis and statistics for plagioclase in monzonitic granite (DT-37)
颗粒(单体) 双晶律及其复合关系 双晶中单体接触情况 双晶形式描述 1(1, 2, 3) 颗粒中以单体1为主,单体2和3以晶畴形式零散分布在单体1内部 无聚片,主晶-晶畴为卡斯巴律和卡-钠复合律 2(1, 2, 3, 4) 颗粒中以单体2和3为主,单体1以晶畴形式零散分布在单体2内部,单体4以晶畴形式零散分布在单体3内部.单体2-3的接合面是(010) 聚片为钠长石律,主晶-晶畴为卡-钠复合律,卡斯巴律基本不接触 3(1, 2, 3, 4) 颗粒中以单体1和2为主,单体3、4以晶畴形式零散分布在单体2的内部.单体1-2的接合面是(010) 聚片为卡斯巴律,主晶-晶畴为钠长石律和卡-钠复合律 4(1, 2) 颗粒中以单体1为主,单体2以晶畴形式零散分布在单体1内部 无聚片,主晶-晶畴为卡-钠复合律 5 (1, 2, 3, 4) 颗粒中以单体1和2为主,单体4以晶畴形式零散分布在单体1内部,单体3以晶畴形式零散分布在单体2内部.单体1-2的接合面是(010) 聚片为钠长石律,主晶-晶畴为卡-钠复合律,卡斯巴律基本不接触 6(1, 2, 3) 颗粒中以单体1和2为主,单体3以晶畴形式零散分布在单体1的内部.但单体1-2的接合面不是(010)而是(h0l),所以单体1和2是肖钠长石律 聚片为肖钠长石律,主晶-晶畴为卡-钠复合律,卡斯巴律基本不接触 7(1, 2) 颗粒中以单体1和2为主.单体1和2的接合面是(010) 聚片为钠长石律,无晶畴 8(1, 2) 颗粒中以单体1和2为主.单体1-2的接合面是(010) 聚片为钠长石律,无晶畴 9(1, 2, 3, 4) 颗粒中以单体1和2为主,单体4以晶畴形式零散分布在单体1内部,单体3以晶畴形式零散分布在单体2内部.单体1-2接合面是(010) 聚片为钠长石律,主晶-晶畴为卡-钠复合律,卡斯巴律基本不接触 10(1, 2, 3, 4) 颗粒中以单体2为主,单体1、3、4以晶畴形式零散分布在单体2内部.单体2-4的接合面大致为(010) 聚片为钠长石律,主晶-晶畴为卡斯巴律和卡-钠复合律 11(1, 2, 3) 颗粒中以单体1和2为主,单体3以晶畴的形式分布在单体2中.单体1-2的接合面是(010) 聚片为钠长石律,主晶-晶畴为卡-钠复合律,卡斯巴律基本不接触 注:实线表示钠长石律(Ab);虚线表示卡斯巴律(Cd);点划线表示卡-钠复合律(Ab-Cd). 表 5 二长闪长岩(DT-24)样品中斜长石双晶测试分析统计
Table 5. Twin analysis and statistics for plagioclase in monzonitic diorite (DT-24)
颗粒(单体) 双晶律及其复合关系 双晶中单体接触情况 双晶形式描述 1(1, 2, 3, 4) 颗粒中以单体1为主,单体2-3交织形成另一个聚片,单体4以晶畴形式零散分布在单体1的内部.单体1与单体2-3的接合面是(010) 聚片为钠长石律,主晶-晶畴为卡-钠复合律,卡斯巴律基本不接触 2(1, 2, 3, 4, 5) 颗粒中以单体3和4为主,单体1以晶畴形式零散分布在单体3的内部,单体2以晶畴形式零散分布在单体4的内部.单体3-4的接合面是(010).单体5很少量,主要以晶畴形式分布在单体1中 聚片为卡斯巴律,主晶-晶畴为卡-钠复合律,钠长石律基本不接触 1-2-3-4-5共 < 001 > ,且3-4-5之间形成另一种复合双晶 3(1, 2, 3, 4) 颗粒中以单体1和2为主,单体4以晶畴形式零散分布在单体1的内部,单体3以晶畴形式零散分布在单体2的内部.单体1-2的接合面是(010) 聚片为钠长石律,主晶-晶畴为卡-钠复合律,卡斯巴律基本不接触 4(1, 2, 3) 颗粒中以单体1为主,单体2、3以晶畴形式零散分布在单体1的内部 无聚片,主晶-晶畴为卡斯巴律和卡-钠复合律 5(1, 2, 3, 4) 颗粒中以单体1为主,单体2、3、4交叉在一起(类似于主晶-晶畴的关系) 无聚片.主晶-晶畴为钠长石律、卡斯巴律和卡-钠复合律 6(1, 2) 颗粒中以单体1为主,单体2以晶畴形式零散分布在单体1的内部 无聚片,主晶-晶畴为卡斯巴律 7(1, 2, 3, 4) 颗粒中以单体1和2为主,单体3、4、1以晶畴形式零散分布在单体2的内部.单体1-2的接合面是(010) 无聚片,主晶-晶畴为卡斯巴律、卡-钠复合律和钠长石律 8(1, 2, 3, 4) 颗粒中以单体1和2为主,单体2和3交织形成一个聚片, 单体4很少,以晶畴分布在1和2中.单体1-2的接合面是(010) 聚片为卡斯巴律,主晶-晶畴为卡-钠复合律和钠长石律 9(1, 2, 3, 4, 5, 6, 7, 8) 颗粒中以单体6为主,单体1、2以晶畴形式零散分布于单体6中.单体5很少 无聚片,主晶-晶畴为卡斯巴律和钠长石律 另一个区域单体3、4和7交织在一起,单体8在3和4中两个区界面方向性不好.两个区内部各单体界面也不清楚,无方向性 注:实线表示钠长石律(Ab);虚线表示卡斯巴律(Cd);点划线表示卡-钠复合律(Ab-Cd). 表 6 二长变粒岩(HA-17)样品中斜长石双晶测试分析统计
Table 6. Twin analysis and statistics for plagioclase in monzonitic leptite (HA-17)
颗粒(单体) 双晶律及其复合关系 双晶中单体接触情况 双晶形式描述 1(1, 2, 3, 4) 颗粒中以单体1和4为主,单体2以晶畴形式零散分布在单体1的内部,单体3以晶畴形式零散分布在单体4的内部.单体1-4的接合面是(010) 聚片为钠长石律,主晶-晶畴为卡-钠复合律,卡斯巴律基本不接触 2(1, 2, 3, 4, 5, 6) 颗粒中以单体1和5为主,单体2、3、4以晶畴形式零散分布在单体1的内部,单体6以晶畴形式零散分布在单体5的内部.单体1-5的接合面是(010) 聚片为卡斯巴律,主晶-晶畴为卡-钠复合律,钠长石律基本不接触 3(1, 2, 3, 4) 颗粒中以单体1和3为主,单体2以晶畴形式零散分布在单体1的内部,单体4以晶畴形式零散分布在单体3的内部.单体1-3的接合面是(010) 聚片为钠长石律,主晶-晶畴为卡-钠复合律,卡斯巴律基本不接触 4(1, 2, 3) 颗粒中以单体1和2为主,单体3以晶畴形式零散分布在单体1的内部.单体1-2的接合面是(010),单体2-3基本不接触 聚片为卡斯巴律,主晶-晶畴为卡-钠复合律,钠长石律基本不接触 5(1, 2, 3, 4) 颗粒中以单体2和3为主,单体1以晶畴形式零散分布在单体2的内部,单体4以晶畴形式零散分布在单体3的内部.单体2-3的接合面是(010) 聚片为钠长石律,主晶-晶畴为卡-钠复合律,卡斯巴律基本不接触 6(1, 2, 3, 4, 5, 6) 颗粒中以单体1和2为主,单体4以晶畴形式零散分布在单体3的内部,单体1-2局部沿(010)方向规则接触 聚片为卡-钠复合律,主晶-晶畴也为卡-钠复合律 单体1-2-3-4中存在三种双晶律,组成一个具三-六方对称的规则连生体 5-6为钠长石律,单体5很少,接触关系不明确 7(1, 2) 颗粒中以单体1和2为主.单体1-2的接合面是(010) 聚片为钠长石律,无晶畴 8(1, 2, 3) 颗粒中以单体1和2为主,单体3以晶畴形式零散分布在单体2的内部.单体1-2的接合面是(010) 聚片为钠长石律,主晶-晶畴为卡-钠复合律,卡斯巴律基本不接触 9(1, 2) 颗粒中以单体1和2为主.单体1-2的接合面是(010) 聚片为钠长石律,无晶畴 注:实线表示钠长石律(Ab);虚线表示卡斯巴律(Cd);点划线表示卡-钠复合律(Ab-Cd). -
Arzilli, F., Mancini, L., Voltolini, M., et al., 2015. Near-Liquidus Growth of Feldspar Spherulites in Trachytic Melts: 3D Morphologies and Implications in Crystallization Mechanisms. Lithos, 216/217: 93-105. https://doi.org/10.1016/j.lithos.2014.12.003 Balić-Žunić, T., Piazolo, S., Katerinopoulou, A., et al., 2013. Full Analysis of Feldspar Texture and Crystal Structure by Combining X-Ray and Electron Techniques. American Mineralogist, 98: 41-52. doi: 10.2138/am.2013.4124 Brown, W.L., Macaudière, J., 1986. Mechanical Twinning of Plagioclase in a Deformed Meta-Anorthosite—The Production of M-Twinning. Contributions to Mineralogy and Petrology, 92(1): 44-56. https://doi.org/10.1007/BF00373962 Brugger, C.R., Hammer, J.E., 2015. Prevalence of Growth Twins among Anhedral Plagioclase Microlites. American Mineralogist, 100(2/3): 385-395. https://doi.org/10.2138/am-2015-4809 Chi, J.S., Wu, G.Z., 1982. Federov Law. Geological Publishing House, Beijing (in Chinese). Deer, W.A., Howie, R.A., Zussman, J., 2001. Rock-Forming Minerals (Volume 4A)-Framework Silicates: Feldspar. 2nd ed. Geological Society Publishing House, London. Hu, C.Q., 1991. Measurement of Plagioclase Composition and Structural State by Using an Improved Twin Operation Method. Journal of Guilin College of Geology, 11(3): 315-319(in Chinese with English abstract). Jiang, X.P., 1985. Using a Triaxlal Spindle Stage to Determine the Chemical Composition Structure Op and Twinning Type of Plagioclase. Yunnan Geology, 4(3): 281-290(in Chinese with English abstract). Lee, M.R., 2010. Transmission Electron Microscopy (TEM) of Earth and Planetary Materials: A Review. Mineralogical Magazine, 74(1): 1-27. https://doi.org/10.1180/minmag.2010.074.1.1 Noguchi, T., 2013. Importance of Transmission Electron Microscopy (TEM) on the Studies of Planetary Materials and the Progress of TEM and Peripheral Technology. Abstracts of Meeting of the Geochemical Society of Japan, 60: 252-253. https://www.sciencedirect.com/science/article/pii/S0080878408626794 Shen, S.Y., 1990. The Recognition of Plagioclase Twins with Universal Stage Method. Journal of Mineralogy and Petrology, 10(3): 33-40(in Chinese with English abstract). Smith, J.V., Brown, W.L., 1988. Feldspar Minerals, Volume 1: Crystal Structures, Physical, Chemical and Microtextural Properties. Springer-Verlag, Berlin Heidelberg. Wang, C.B., Chen, T.L., Chen, N., 2011. The Origin of Iridescent Plagioclase from Finland: A Perspective from the Relationship between the Inclusions and the Iridescence. Acta Petrologica et Mineralogica, 30(1): 150-160(in Chinese with English abstract). Xu, C., Zhao, S.R., Li, C., et al., 2016. Plagioclase Twins in a Basalt: An Electron Backscatter Diffraction Study. Journal of Applied Crystallography, 49(6): 2145-2154. https://doi.org/10.1107/s1600576716015739 Xu, H.J., Jin, S.Y., Zheng, B.R., 2007. New Technique of Petrofabric: Electron Backscatter Diffraction(EBSD). Geoscience, 21(2): 213-225(in Chinese with English abstract). Zhang, R.X., Yang, S.Y., 2016. A Mathematical Model for Determining Carbon Coating Thickness and Its Application in Electron Probe Microanalysis. Microscopy and Microanalysis, 22(6): 1374-1380. https://doi.org/10.1017/s143192761601182x 池际尚, 吴国忠, 1982. 弗德罗夫法. 北京: 地质出版社. 胡承绮, 1991. 一种测定斜长石成分和结构态的改进双晶法. 桂林冶金地质学院学报, 11(3): 315-319. https://www.cnki.com.cn/Article/CJFDTOTAL-GLGX199103010.htm 江鑫培, 1985. 三轴旋转针台测定斜长石成分结构状态和双晶类型. 云南地质, 4(3): 281-290. https://www.cnki.com.cn/Article/CJFDTOTAL-YNZD198503005.htm 沈上越, 1990. 旋转台法鉴别斜长石双晶律. 矿物岩石, 10(3): 33-40. https://www.cnki.com.cn/Article/CJFDTOTAL-KWYS199003004.htm 王晨波, 陈廷礼, 陈南, 2011. 芬兰晕彩斜长石晕彩成因探讨: 包裹体及其与晕彩的关系. 岩石矿物学杂志, 30(1): 150-160. doi: 10.3969/j.issn.1000-6524.2011.01.015 徐海军, 金淑燕, 郑伯让, 2007. 岩石组构学研究的最新技术——电子背散射衍射(EBSD). 现代地质, 21(2): 213-225. doi: 10.3969/j.issn.1000-8527.2007.02.005