关键词: 显微构造, 糜棱岩, 构造变形环境, 秦岭带

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