北喜马拉雅穹隆带然巴韧性剪切带石英动态重结晶颗粒的分维几何分析与主要流变参数的估算

位于北喜马拉雅穹隆带东段的然巴构造穹隆外围发育环形韧性剪切带,带内岩石经韧性剪切形成各类糜棱状岩石。石英为带内变形岩中最为常见的造岩矿物,在不同的温度、应变速率下产生不同的显微构造,其中动态重结晶最为常见。重结晶新晶颗粒边界普遍具有锯齿状或港湾状结构,是应变和变形环境的天然记录。新晶粒分维几何统计分析表明:带内动态重结晶石英颗粒边界形态具有自相似性(1≤D≤2),表现出分形特征,分维数值为1.14～1.19,变形温度大约500℃。同构造变质环境属中——高绿片岩相;初步估算古应变速率可能低于10-9.5S-1;根据重结晶粒径估算变形古应力6.2～58.8MPa。

FRACTAL ANALYSIS OF DYNAMICALLY RECRYSTALLIZED QUARTZ GRAINS AND ESTIMATION OF MAINLY RHEOLOGICAL PARAMETERS OF THE RANBA DUCTILE SHEAR ZONE, NORTHERN HIMALAYAN DOME BELT

A ductile shear zone developed around the Ranba dome in the eastern part of northern Himalayan dome belt. Various mylonites were formed in this ductile shear zone, in which the quartz was one of the major rock-making minerals. Different microstructures developed in the quartz under different temperatures and strain rates, among which dynamic recrystallization was the most common structure. The shapes of recrystallized quartz grains with their jagged and indented boundaries were natural records of deformation conditions. Fractal analysis showed that the boundaries of recrystallized grains had statistically self-similarities with the numbers of fractal dimension from 1.14 to 1.19. From these numbers, deformation temperature was about 500℃, similar to that of middle or high green-schist grade metamorphism. Paleo-strain rates were deduced to be not more than 10^-9.5S^-1, and the paleo-stress was calculated with grain size of recrystallized quartz to be 6.2～58.8 MPa.