舒兰韧性剪切带应变分析及石英动态重结晶颗粒分形特征与流变参数估算

舒兰北东向韧性剪切带位于佳木斯-伊通断裂带(佳-伊断裂带)中南段, 剪切带内糜棱岩具有明显左行走滑特征, 片麻理产状近NNE向.糜棱岩中长石有限应变Flinn图解判别岩石类型为L-S型构造岩, 属拉长型应变.石英C轴EBSD组构分析表明, 石英组构以中低温菱面为主, 滑移系为{0001} < 110>.剪切带内糜棱岩的剪应变为0.44, 不同方法计算所得运动学涡度值均大于0.95, 指示剪切变形以简单剪切为主.综合矿物变形温度计、石英C轴EBSD组构、石英的粒度-频数图及Kruhl温度计综合估计该韧性剪切带变形机制以位错蠕变机制为主, 变质相为低绿片岩相, 发生韧性变形和糜棱岩化温度范围在400~500 ℃之间.糜棱岩内石英动态重结晶新晶粒边界普遍具有锯齿状或港湾状结构, 利用分形方法对其重结晶新晶边界研究表明, 这些晶粒边界具有自相似性, 表现出分形特征, 分形维数值为1.195~1.220.根据石英重结晶粒径估算差应力值为24.35~27.59 MPa, 代表了舒兰韧性剪切带糜棱岩化作用过程的差异应力下限.使用不同实验方法估算、比较和分析了该剪切带古应变速率, 认为该速率应为10-12.00~10-13.18 s-1, 与区域性应变速率10-13.00~10-15.00 s-1对比, 说明舒兰韧性剪切带的应变速率与世界上大多数韧性剪切带中的糜棱岩应变速率一致, 是缓慢变形的结果, 其形成可能与早白垩世伊泽纳崎板块向欧亚大陆俯冲发生转向有关. 

Strain and Fractal Analysis of Dynamically Recrystallized Quartz Grains and Rheological Parameter Estimation of Shulan Ductile Shear Zone

Shulan ductile shear zone represents a suit of mylonites with sinistral strike-slip characteristics and NNE gneissosity located in south-middle part of the Jiamusi-Yitong fault (called Jia-Yi fault in short). Systematic measurement of the finite strains of feldspar in mylonites indicates that the strain type is extension strain in L-S tectonites. Quartz C-axis EBSD fabric indicates that the quartz fabrics is mainly low-middle temperature prism-glide fabrics with slip system of {0001} < 110>. By calculation of micro structures and quartz C-axis fabrics, it is found that the shearing strain is 0.44; all kinematic vorticities are all more than 0.95, which indicates that the deformation is mainly simple shear. Mineral deformation behaviors, quartz C-axis EBSD fabrics, quartz grain size-frequency diagram and Kruhl thermometer demonstrate that the ductile shear zone was developed under a condition of low-grade greenschist facies, with deformation temperatures ranging from 400 to 500 ℃, and dislocation creep is the main deformation mechanism. The shapes of recrystallized quartz grains in mylonites with their jagged and indented boundaries are natural records of deformation conditions. Fractal analysis shows that the boundaries of recrystallized grains have statistically self-similarities with the numbers of fractal dimension from 1.195 to 1.220. The paleo-stress from dynamically recrystallized grain sizes of quartz are 24.35-27.59 MPa, representing the lower limit of the paleo-stress during mylonization. Together with temperature estimates and applying published flow laws, it is concluded that estimated strain rates on the order of 10-12.00 to 10-13.18 s-1, contrasting with regional strain rate of 10-13.00 to 10-15.00 s-1, indicate deformation of mylonite in Shulan ductile shear zone with low strain rates which are consistent with most other ductile zone, suggest the deformation is slow process. Taking into consideration of the regional tectonic setting of NE China, we suggest that the formation of the ductile shear zone with NNE trending might be related to moving direction changing of the Izanagi plate obliquely subducting under the Eurasia plate.