Characterization of Micro-Texture of Quartz Mylonite Deformation Process Using Fractal P-A Model
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摘要: 定量度量动力变质作用下组成糜棱岩矿物颗粒的不规则变化是一项挑战性的研究.以基于GIS的P-A (周长-面积) 模型定量地描述糜棱岩中具自相似性石英形态的不规则变化.研究实例是苏格兰西北地区Moine逆冲断裂带前缘变质程度不同的5种类型的糜棱岩.石英是糜棱岩的主要矿物成分, 其镜下的显微图片经扫描转换成数字图像, 再通过GIS技术转换成矢量图, 并计算出每颗石英的周长和面积.研究结果表明, 随变质程度的增加, 其P-A分形维数分别从1.20、1.28、1.38、1.46, 逐步增加到1.60.这表明, 随变质程度的增加, 变形程度与动态重结晶作用加强, 石英颗粒从规则到不规则.Abstract: Quantifying the degree of quartz mylonite deformation, including the irregularities of the frequency distribution of the minerals involved, is one of the most challenging areas in mylonite analysis. Fractal modelling is here demonstrated to be an effective means to achieve this goal. The P-A (perimeter-area) model is used to quantify the irregularities of quartz, the main mineral component of mylonite, in the geometries. Five types of mylonites with different degrees of deformation within the foreland of the Moine thrust zone in NW Scotland were selected. The quartz was extracted from digital photomicrographs of multiscale-grey image grid data, and converted into vector data. The areas and perimeters of these quartz grains were calculated by GIS-based technologies. There is an increase in the degree of deformation of mylonite from type 1 to type 5, a D_ AP (the perimeter-area fractal dimension) increase from 1.20, 1.28, 1.38, 1.46 to 1.60, respectively. The results indicate quantitatively that quartz grains change from a regular to an irregular shape.
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Key words:
- fractal model /
- micro-texture /
- quartz /
- mylonite /
- deformation
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图 1 糜棱岩显微图片
图片a、b、c、d和e分别对应糜棱岩类型1、2、3、4和5;图片是垂直于叶理、平行于线理方向拍摄，正交偏光
Fig. 1. Micrographs of mylonites of five types(Law et al., 1986)
图 2 GIS技术处理石英的显微图像过程
a.糜棱岩类型2的原始图片; b.等高线图中灰度值为180时圈定的石英颗粒; c.用GIS技术从a中提取石英颗粒的矢量图; d.c叠加在a上, 以显示二者的差别
Fig. 2. GIS-based technique for processing micrographs of quartz grains
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