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

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