钦杭结合带(南段)庞西垌断裂中动态重结晶石英颗粒分形特征及主要流变参数估算

广东庞西垌断裂带发育于钦杭结合带南段,是控制该区域银金矿床的重要构造,也是钦杭结合带构造演化的重要窗口。分析了庞西垌断裂带中心发育的糜棱岩及其内动态重结晶石英颗粒分形特征及主要流变参数。研究显示,庞西垌断裂带糜棱岩中可以观察到典型的S-C组构。σ型旋转碎斑系指示北东向韧性剪切带经历了右行剪切。在显微镜下,可以观察到矿物颗粒表现出波状消光、核幔构造、亚晶粒化、动态重结晶、单晶拉长及石英晶条带等现象。石英颗粒的动态重结晶作用十分普遍。单个石英晶粒表现为拉长状、锯齿状、港湾状等不规则状边界形态。整体上石英晶粒表现出微弱的定向趋势。根据分形法估算得到的变形温度,结合显微镜下观察的矿物特征,推断庞西垌断裂带内岩石韧性变形温度在600℃左右,相当于低角闪岩相。石英的"重结晶颗粒粒径压力计"估算得到古差异应力下限在9.1～10.7 MPa之间。石英岩的实验高温流变率显示,应变速率应低于10-13.8S-1。这些流变参数可以利用来加深对断裂带韧性变形过程的认识。

Fractal Feature of Dynamically Recrystallized Quartz Grains and Estimation of Mainly Rheological Parameters in Pangxidong Fracture Zone, Southern Section of Qinzhou Bay-Hangzhou Bay Juncture Orogenic Belt, South China

The Pangxidong fracture zone of Guangdong developing in south of Qinzhou Bay(Q)-Hangzhou Bay(H) juncture orogenic belt is an important structure controlling silver-gold deposits forming and also a significant window to see the tectonic evolution history of Q-H juncture orogenic belt. The mylonites from it are studied in this paper. It researches the fractal feature and mainly rheological parameters of dynamically recrystallized quartz grains in mylonites. Classical S-C fabrics are founded in mylonites. This NE-trending ductile shear zone is dextral shear according to studying σ-rotational porphyroclasts. Under the light microscope, undulatory extinction, core-mantle structure, sub grain, dynamic recrystallization, elongated single crystal and quartz ribbon are observed. The widespread dynamic recrystallization of quartz grains which are slightly elongated and directed have jagged and indented boundaries. The ductile deformation temperature of rocks in Pangxidong fracture zone is approximately 600℃ through fractal analysis and microscope observation, which presents low amphibolite facies. The quartz recrystallized grain size paleopiezometer suggests that the differential stress is 9.1-10.7MPa(lower limits). The extrapolation of quartzite flow laws shows the strain rate is under 10^-13.8s^-1. These rheological parameters can be used in a deeper research on the ductile deformation process of Pangxidong fracture zone.