Abstract: The Red River Fault zone is an inter-block tectonic deformation belt which has experienced long-term tectonic evolution.On the southwest of the fault zone,a suit of mylonites is exposed which was formed by ductile shear.In the study area,the mylonite exhibits many kinds of macroscopic deformation structures,such as planar lamination,linear lamination,and S-C fabric.Its microscopic deformation is characterized by mica fish,feldspar mortar,flaser and extension of feldspar and amphibole,and pressure shadow produced by mortar rotation.In particular,the quartz has experienced widespread deformation,resulting in wavy extinction,core-mantle structure,dynamic recrystallization,flaser and extension of single grain,and quartz fringe.The new quartz grain by recrystallization is well developed,of which the boundary has microscopic features of saw-toothed or embayed shape.These distinct features record the temperature-pressure conditions and rheological rates for deformation.Analysis of fractal dimension to the quartz grain shows that the boundary shapes of recrystallization grain of quartz have self-similarity,presenting a fractal feature,with values of fractal dimension 1.150～1.180,and deformation temperature about 500℃.The tectonic metamorphic condition is of high-greenschist facies and low-amphibole facies.It is estimated that the strain rate is probably less than 10^-8.4s^-1,and the paleo-stress for deformation is 42.0～58.0MPa based on grain size of recrystallization.

Key words: Red River Fault, mylonite, quartz, dynamic recrystallization, strain rate, fractal dimension

摘要： 红河断裂带是一条经历了长期构造演化的块间构造变形带,该断裂的西南侧出露一套经韧性剪切形成的糜棱岩。研究区糜棱岩宏观上发育多种变形组构,如构造面理、线理、S-C组构等。微观变形特征有云母鱼、长石碎斑、长石和角闪石压扁拉长、碎斑旋转形成的压力影等;尤其是石英普遍变形,其特征有波状消光、核幔构造、动态重结晶、单颗粒压扁拉长及石英条带等;石英动态重结晶新颗粒尤其发育,重结晶的新颗粒边界具有锯齿状或港湾状等不同的微观特征,这些不同的特征记录了变形时的温压环境和流变速率。石英新颗粒分维几何统计分析表明:研究区石英动态重结晶颗粒边界形态具有自相似性,表现出分形特征。分维数值为1.150～1.180,变形温度大约500℃,同构造变质环境属高绿片岩相-低角闪岩相;初步估算应变速率可能低于10^-8.4s^-1,根据石英重结晶的粒径估算变形古应力为42.0～58.0MPa。

关键词: 红河断裂, 糜棱岩, 石英, 动态重结晶, 应变速率, 分形维数