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
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摘要
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。
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 10-7.27 s-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℃).
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 10-7.27 s-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℃).
引文
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[18]Xiang B W,Wang Y S,Li C C,et al.Evolution of the Xiaotian-Mozitan fault and its implications for exhumation of Dabie HP-UHP rocks[J].Progress in Natural Science,2008,18(6):713-722.
[19]向必伟,王勇生,朱光.晓天—磨子潭断裂糜棱岩化过程的温压环境及其指示意义[J].矿物学报,2008,28(2):161-168.Xiang Biwei,Wang Yongsheng,Zhu Guang.Acta Mineralogica Sinica,2008,28(2):161-168.
[20]Twiss R J,Moores E M.Structural geology[M].2nd ed.New York:W H Freeman&Company,2007.
[21]Stipp M,Stünitz H,Heilbronner R,et al.Dynamic recrystallization of quartz:Correlation between natural and experimental conditions[J]//de Meer S,Drury M R,de Bresser J H P,et al.Deformation Mechanisms,Rheology and Tectonics:Current Status and Future Perspectives,London:Geological Society Special Publications,2002:171-190.
[2]王新社,郑亚东,杨崇辉,等.用动态重结晶石英颗粒的分形确定变形温度及应变速率[J].岩石矿物学杂志,2001,20(1):36-41.Wang Xinshe,Zheng Yadong,Yang Chonghui,et al.Acta Petrologica et Mineralogica,2001,20(1):36-41.
[3]张波,张进江,郭磊.北喜马拉雅穹隆带然巴韧性剪切带石英动态重结晶颗粒的分维几何分析与主要流变参数的估算[J].地质科学,2006,41(1):158-169.Zhang Bo,Zhang Jinjiang,Guo Lei.Scientia Geologica Sinica,2006,41(1):158-169.
[4]Kruhl J H,Nega M.The fractal shape of sutured quartz grain boundaries:Application as a geothermometer[J].International Journal of Earth Sciences,1996,85(1):38-43.
[5]Takahashi M,Nagahama H,Masuda T,et al.Fractal analysis of experimentally,dynamically recrystallized quartz grains and its possible application as a strain rate meter[J].Journal of Structural Geology,1998,20(2-3):269-275.
[6]Mamtani M.Strain-rate estimation using fractal analysis of quartz grains in naturally deformed rocks[J].Journal of the Geological Society of India,2010,75(1):202-209.
[7]吴小奇,刘德良,李振生,等.确定变形温度和应变速率分形法的探讨——以郯庐断裂浮槎山构造岩为例[J].中国地质,2006,33(1):153-159.Wu Xiaoqi,Liu Deliang,Li Zhensheng,et al.Geology in China,2006,33(1):153-159.
[8]张秉良,刘瑞珣,向宏发,等.红河断裂带中南段糜棱岩分形特征及主要流变参数的估算[J].地震地质,2008,30(2):473-483.Zhang Bingliang,Liu Ruixun,Xiang Hongfa,et al.Seismology and Geology,2008,30(2):473-483.
[9]汤加富,周存亭,侯明金,等.大别山及邻区地质构造特征与形成演化:地幔差速环流与陆内多期造山[M].北京:地质出版社,2003.Tang Jiafu,Zhou Cunting,Hou Mingjin,et al.The geological characteristics,formation and evolution of Dabie mountains and its adjacent regions[M].Beijing:Geological Publishing House,2003.
[10]Stipp M,Stünitz H,Heilbronner R,et al.The eastern Tonale fault zone:A"natural laboratory"for crystal plastic deformation of quartz over a temperature range from250to700°C[J].Journal of Structural Geology,2002,24(12):1861-1884.
[11]Hacker B,Yin A,Christie J,et al.Differential stress,strain rate,and temperatures of mylonitization in the Ruby Mountains,Nevada:Implications for the rate and duration of uplift[J].Journal of Geophysical Research,1990,95(B6):8569-8580.
[12]Koch P S.Rheology and microstructures of experimentally deformed quartz aggregates[D].Los Angeles,CA:University of California,1983.
[13]Twiss R J.Theory and applicability of a recrystallized grain size paleopiezometer[J].Pure and Applied Geophysics,1977,115(1):227-244.
[14]Twiss R J.Static theory of size variation with stress for subgrains and dynamically recrystallized grains[C]//Magnitude of Deviatoric Stresses in the Earth's Crust and Upper Mantle:Proceedings of Conference IX:Convened Under Auspices of National Earthquake Hazards Reduction Program.Menlo Park,CA:US Geological Survey,1980,80(625):665-683.
[15]Mercier J C C,Anderson D A,Carter N L.Stress in the lithosphere:Inferences from steady state flow of rocks[J].Pure and Applied Geophysics,1977,115(1):199-226.
[16]Koch P S,Christie J M,Ord A,et al.Effect of water on the rheology of experimentally deformed quartzite[J].Journal of Geophysical Research:Solid Earth,1989,94(B10):13975-13996.
[17]Parrish D K,Krivz A L,Carter N L.Finite-element folds of similar geometry[J].Tectonophysics,1976,32(3-4):183-207.
[18]Xiang B W,Wang Y S,Li C C,et al.Evolution of the Xiaotian-Mozitan fault and its implications for exhumation of Dabie HP-UHP rocks[J].Progress in Natural Science,2008,18(6):713-722.
[19]向必伟,王勇生,朱光.晓天—磨子潭断裂糜棱岩化过程的温压环境及其指示意义[J].矿物学报,2008,28(2):161-168.Xiang Biwei,Wang Yongsheng,Zhu Guang.Acta Mineralogica Sinica,2008,28(2):161-168.
[20]Twiss R J,Moores E M.Structural geology[M].2nd ed.New York:W H Freeman&Company,2007.
[21]Stipp M,Stünitz H,Heilbronner R,et al.Dynamic recrystallization of quartz:Correlation between natural and experimental conditions[J]//de Meer S,Drury M R,de Bresser J H P,et al.Deformation Mechanisms,Rheology and Tectonics:Current Status and Future Perspectives,London:Geological Society Special Publications,2002:171-190.
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