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

Liang Chenyue; Liu Yongjiang; Meng Jingyao; Wen Quanbo; Li Weimin; Zhao Yingli; Mi Xiaonan; Zhang Li

doi:10.3799/dqkx.2015.008

Abstract：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 in-dicates that the quartz fabrics is mainly low-middle temperature prism-glide fabrics with slip system of {0001}<1 10>.By cal-culation 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 devel-oped under a condition of low-grade greenschist facies,with deformation temperatures ranging from 400 to 500 ℃,and disloca-tion creep is the main deformation mechanism.The shapes of recrystallized quartz grains in mylonites with their jagged and in-dented 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 1.1 95 to 1.220.The paleo-stress from dy-namically recrystallized grain sizes of quartz are 24.35-27.59 MPa,representing the lower limit of the paleo-stress during myl-onization.Together with temperature estimates and applying published flow laws,it is concluded that estimated strain rates on the order of 10 -1 2.00 to 10 -1 3 .1 8 s-1 ,contrasting with regional strain rate of 10 -1 3 .00 to 10 -1 5 .00 s-1 ,indicate deformation of mylo-nite in Shulan ductile shear zone with low strain rates which are consistent with most other ductile zone,suggest the deforma-tion 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 subduc-ting under the Eurasia plate.