火成岩结构的二维定量化分析方法  

Two dimensional quantitative textural analysis method for igneous rock

作　　者：杨宗锋[1] 李解[1] 姜晓杰 曲林雨 袁野[1] 李英英 彭慧中 饶彤 马犇 徐志豪 YANG Zongfeng;LI Jie;JIANG Xiaojie;QU Linyu;YUAN Ye;LI Yingying;PENG Huizhong;RAO Tong;MA Ben;XU Zhihao(State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质大学(北京)地质过程与矿产资源国家重点实验室,北京100083

出　　处：《地学前缘》2020年第5期23-38,共16页Earth Science Frontiers

基　　金：国家自然科学青年基金项目(41402053);中央高校基本科研优秀教师基金项目(2652019049)。

摘　　要：近些年,定量化火成岩结构研究表明,利用常规的岩矿鉴定设备,获取不同尺度的火成岩二维岩相学照片,通过肉眼识别矿物颗粒,并借助图像处理和结构分析软件,可以准确地量化火成岩的结构特征。本文结合近些年国内外同行的研究成果,对火成岩二维定量化结构分析方法中常用的多种观测方式优缺点进行了总结。粒度在毫米级以下的火成岩的定量化结构参数,可以用偏光显微镜下的透射光、反射光、阴极发光和电子探针背散射成像中的两种或两种以上观测方式进行分析,并具有较高的精度和准确度。粒度小于0.03mm的各种镁铁质矿物可用反射光和背散射图进行分析,灰度近似的镁铁质矿物可以利用图像处理软件赋予不同的彩色,提高颗粒间的辨识度。常规偏光显微镜下不易区分的长英质矿物和多数副矿物可用偏光显微镜阴极发光进行分析。粒度在毫米级以上的造岩矿物可以用光片或野外测量的方式进行定量分析。为了方便相关领域学者使用火成岩二维定量化结构分析方法,本文详细列出了具体的分析步骤,并结合一个玄武岩样品中的橄榄石斑晶数据结果,重点分析以下4个方面的问题:(1)如何准确识别矿物颗粒边界;(2)矿物含量和形态的确定;(3)分析区域面积和颗粒数的确定;(4)不同晶体群的区分。分析结果表明,颗粒数100~500颗时,晶体粒度分布(CSD)的截距和斜率、矿物含量、定向程度和粒状矿物的三轴比在误差范围内没有显著区别,但颗粒最大长度和聚集程度会被低估。当颗粒数小于300颗时,晶体空间聚集程度的R值会被高估0.05~0.2,这一点在以往的研究中没有得到充分重视。当颗粒数大于500颗时,所有结构参数都趋于稳定,且精度和准确度都会显著提高。目前多数研究者提供的结构参数往往与观测和统计方式有关,缺乏对应的原始数据,不方便同行间的对比�In recent years,quantitative textural studies of igneous rock have shown that by using conventional rock and mineral identification equipment,one can obtain two-dimensional petrographic photos of different scales of igneous rock,so that mineral particles can be identified with naked eyes.Furthermore,by using image processing and textural analysis software the textural characteristics of igneous rocks can be accurately quantify.In this paper,we summarized the advantages and disadvantages of various observation methods commonly used in the two-dimensional quantitative textural analysis in igneous petrology.The quantitative textural parameters of igneous rocks with grain size below millimeter level can be analyzed by two or more observation methods using polarized microscope with transmission,reflective light or cathodoluminescence and back scatter-electron imaging techniques to obtain digital images of high precision and accuracy.All kinds of mafic minerals with crystal size less than 0.03 mm can be analyzed by reflective light and back scatter-electron image.One can assign different colors to look-alike gray-scale mafic mineral images by image processing software to improve mineral identification.Polarized microscope cathodoluminescence can be used for the analyses of felsic and most accessory minerals which are difficult to distinguish under conventional polarized microscope.The rock-forming minerals with mm or above grain size can be quantitatively analyzed by polished large sections or field measurement.In order to facilitate researchers in related fields to use this method,we listed the specific analysis steps in detail.Some detailed analyses are made by combining the quantitative textural data of olivine phenocryst in a basalt sample,focusing on how to accurately identify the boundaries of mineral particles,to determine mineral content and shape,analysis area and crystal numbers,and to distinguish different crystal population.The results show that the intercept and slope of crystal size distribution(CSD),mine

关 键 词：火成岩 定量化结构分析 岩相学 晶体粒度分布 偏光显微镜 

分 类 号：P588.1[天文地球—岩石学] TP391.41[天文地球—地质学]