安徽桐城挂车河镇地区东西向韧性剪切带分形特征及其估算应变速率适用性分析

 安徽桐城挂车河镇(挂镇)地区东西向韧性剪切带包括早期长英质韧性主剪切带、晚期镁铁质韧-脆性剪切带和伴生的长英质同向或牵引变形带.两期长英质构造岩中石英动态重结晶新颗粒发育,边界具有锯齿状或港湾状等不同的微观特征,具有统计意义上的自相似性和明显的分形特征.其分形维数介于1.097~1.144,变形温度介于600~700℃,变形条件相当于麻粒岩相和同构造花岗岩;高温流变学方法估算应变速率低于10^-7.27s^-1,镁铁质韧-脆性剪切带伴生初糜棱岩的应变速率比主韧性剪切带糜棱岩的小0.5数量级左右.分形维数可用作变形温度计和应变速率计,但石英颗粒变形实验推导的Kruhl温度计和Takahashi应变速率计在天然变形岩石中应用很少.与其他方法估算的变形温度和应变速率综合对比结果表明,Kruhl温度计是适用的,而Takahashi应变速率计仅适用于低温(T<400℃)条件.

Fractal Analysis of East-West Ductile Shear Zone in Guachehe Town Area,Tongcheng, Anhui and Its Applicability of Strain-rate Estimation

East-West ductile shear zone of Guachehe town, Tongcheng, Anhui consists of early felsic ductile shear zone and later mafic brittle-ductile shear zone associated with synthetic or tractive felsic deformation zone in granite wall-rock. The boundaries of new quartz grains of dynamical recrystallization, which are well-developed in two phases of felsic tectonite, had statistically self-similarity with microscopic features, such as indented or embayed boundary shape. Their area-perimeter fractal dimensions range from 1.097 to 1.144 with the range of deformation temperatures from 600 to 700℃, which is corresponding to granulite facies of metamorphic condition. The strain-rates calculated by rheologic empirical equation are less than 10^-7.27s^-1, and that of the later protomylonite associated with mafic brittle-ductile shear zone is less half order of magnitude than that of early mylonite in main-ductile shear zone. The area-perimeter fractal dimension of quartz grains has earlier been proposed as a strain-rate gauge based on experimental deformation of the quartz aggregates, however this method of fractal analysis has rarely been used to estimate the strain-rate of naturally deformed rocks. In comparison with analysis of other estimation methods, it was concluded that geothermometer proposed by Kruhl is suitable, while the strain-rate equation proposed by Takahashi can be only suitable for lower deformation temperature (T<400℃).