Study On Deformation Duration Of Ductile Shear Zone In Guazhen Area, Tongcheng, Anhui

The Tanlu fault zone and Dabie orogen join at Guache river （viz. Guazhen） area,Tongcheng, eastern margin of the Dabie mountains. There develop NNE-NE and EWductile shear zones in Guazhen area, which respectively belong to Tanlu andXiaotian-Mozitan Fault zone. Thereby, it is a better condition for comparative analysisamong different tectonic systems.EW Xiaotian-Mozitan Fault zone consist of early felsic main ductile shear zone andlate mafic ductile-brittle shear zone, and the latter is often concomitant by synthetic ortractive deformation zone in granite wall-rock. The area-perimeter fractal dimensions ofnew quartz grains of dynamical recrystallization in felsic tectonite were1.097¹.144withdeformation temperature of about600℃to700℃, andthe strain rate estimated byrecrystallization particle size method was10^-9.04S^-110^-9.64S^-1(9.12×10^-10S^-12.29×10^-10S^-1). Thestrain rate of concomitant protomylonite with mafic brittle-ductile shear zone was less halforder of magnitude than that of mylonite in felsic main ductile shear zone. In addition, thestrain rate of one late tectonite by the dislocation density method was3.08×10^-14S^-1. Thestrain rate of NE Tanlu fault zone, whose ductile zones developed during the syn-orogenicperiod and early Cretaceous respectively, was1.3×10^-13S^-16.28×10^-14S^-1by the dislocationdensity method.There are similar regularities during mylonitization of felsic rocks.viz. Volume lossand element migration deepen with the increase of deformation intensity, and the latterindicate gain of SiO₂, K2O and Na2O and loss of Fe₂O₃, CaO and MgO. While it is contraryin mafic rocks in Xiaotian-Mozitan Fault zone, viz. volume gain, SiO₂gain and Fe₂O₃andCaO loss.By data calculated from dislocation density, The deformation duration of two period oftectonites in Tanlu fault zone are respectively7.26million years and1.19².45millionyears（Average of1.82million years）, and that of late tectonite in Xiaotian-Mozitan faultzone is0.85million years. By data calculated from recrystallization particle size, theduration of two period of tectonites in Xiaotian-Mozitan Fault zone are very little, only6.45²2.9years. In general, deformation duration of tectonite in Xiaotian-Mozitan faultzone may be less than that of Tanlu fault zone, and that of late tectonite may be less thanthat of early tectonite in Tanlu fault zone. Some known case study indicated that thedurations were of the order of ten thousand years，while two case study in this work were ofmillions years.