Abstract: Microstructures of quartz and feldspars and quartz fabrics from the Shangdan mylonite zone indicate that from west to east in this zone the structural deformation conditions change from low- greenschist facies to middle- to high- greenschist facies, then become high- greenschist to low- amphibolite facies. Under the deformation condition of low- greenschist facies, quartz is dominated by type Ⅰ quartz ribbons and feldspars are mainly of brittle cracking characteristics. Quartz c- fabrics is of single girdle pattern under this condition. Under the deformation condition of middle- to high- greenschist facies, quartz is dominated by type Ⅱ quartz ribbons. Plagioclase is mostly in the state of brittle cracking flow, but K- feldspar begins to transform to ductile state. Quartz c- fabrics show Y- maxima pattern under this condition. Under deformation of high- greenschist to low- amphibolite facies, quartz is dominated by type Ⅳ quartz ribbons and dynamically recrystallized grains of uniform optical feature and 120° tri- joint point. Plagioclase starts to display characteristics of deformation in brittle- ductile transition state. K- feldspar distinctly displays characteristics of ductile deformation. Quartz c- fabrics show typeⅠcross girdle pattern under this condition.

Key words: Microstructure, Mylonite, Structural deformation condition, Qinling belt

摘要： 商丹糜棱岩带不同区段石英和长石的显微构造及石英组构特征表明,商丹糜棱岩带自西向东构造变形环境显示从低绿片岩相至中-高绿片岩相至高绿片岩相-低角闪岩相的变化规律。低绿片岩相变形环境下,石英多为Ⅰ型条带,长石主要显示脆性破裂特征,石英c 轴组构呈单一环带型式。中-高绿片岩相变形环境下,石英主要为Ⅱ型石英多晶条带,斜长石主要处于脆性碎裂流动状态,钾长石开始向韧性转化,石英c轴组构呈绕y 轴分布的点极密型式。高绿片岩相-低角闪岩相变形环境下,石英普遍呈现光性均匀并有120°三连点的动态重结晶和Ⅳ型条带,斜长石开始显示脆-韧性过渡状态的变形特点,钾长石显示明显的韧性变形特点,石英c 轴组构呈Ⅰ型交叉环带型式。

关键词: 显微构造, 糜棱岩, 构造变形环境, 秦岭带