今天是2018年01月17日

内蒙古大青山高级变质岩韧性剪切带及其流变机制

DOI:10.3799/dqkx.2017.135

作者:刘正宏,潘博文,李鹏川,朱 凯,董晓杰

联系地址:吉林大学地球科学学院,吉林长春 130061

摘要:大青山高级变质岩不仅记录华北克拉通早期大陆形成演化历史,也保留了中下部地壳岩石流变信息,它们经历了下部地壳构造层次高角闪岩相-麻粒岩相条件变质变形、深熔作用改造,形成了复杂构造样式和构造要素组合.韧性剪切带是高级变质岩中主要构造形迹,控制着早前寒武纪高级变质岩主体构造格架.依据野外地质产状、变形特征与构造要素叠加改造关系,韧性剪切带划分为早期近水平顺层伸展型和晚期陡倾韧性剪切带.近水平顺层伸展韧性剪切带呈残留状保留在后期变形改造较弱部位上,主要沿着不同地质单元或者岩性层界面上发育,是在伸展变形体制下形成的.晚期陡倾韧性剪切带呈近东西方向展布,规模较大,叠加和改造早期构造形迹,形成于晚期造山挤压构造环境中,以左行滑移为主.这两种韧性剪切带都形成于地壳中深部构造层次高角闪岩相-麻粒岩相条件下,变形机制主要为熔体增强颗粒边界扩散和颗粒流动,使岩石发生大规模的塑性流动.在宏观上形成了不对称流动组构、条纹条带构造、熔融线理、层内流动褶皱等构造形迹,在微观上矿物晶体没有发生明显塑性变形,均匀消光,晶体为三边平衡结构,与静态变质结构相似,形成了地壳深部构造层次上变质构造岩-构造片麻岩.

关键字:大青山;高级变质岩;韧性剪切带;流变机制;构造片麻岩;变质岩;岩石学.

Ductile Shear Zone in High-Grade Metamorphic Rocks and Its Rheomorphic Mechanism in the Daqing Mountain Area, Inner Mongolia

Author:Liu Zhenghong, Pan Bowen, Li Pengchuan, Zhu Kai, Dong Xiaojie

Author Address:College of Earth Sciences, Jilin University, Changchun 130061, China

Abstract:The high-grade metamorphic rocks in Daqing Mountain area not only record the early formation and evolution of the North China craton, but also retain rheomorphic characteristics in the middle-lower crust. These rocks undergwent metamorphism, deformation and anatexis of high amphibolite facies-granulite facies in the lower crust, forming the complex structure styles and association of structural elements. As the main structural feature in the high-grade metamorphic rocks, the ductile shear zones controlled the major tectonic framework of Pre-Cambrian highgrade metamorphic rocks in this area. According to the superimposed reformation between the geological occurrence and deformed deformation characteristics with the structural elements, the ductile shear zones are divided into early subhorizontal bedding extension type and later steep type. The subhorizontal bedding extension ductile shear zone remained at the locations that experienced weak-deformation in later stage. They formed along interfaces of different geological bodies and lithologies under an extensional deformation system. The later steep ductile shear zone was distributed in near EW direction with a larger scale. It formed in the later orogenic compressional environment and reformed the early structural features. These two types of ductile shear zone were both formed under the high amphibolite facies-granulite facies metamorphism in the middle-lower crust. And, the mian deformation is the melt-enhanced grain side diffusion and the grain flow, which caused a large scale plastic flow of the rocks. Some macrostructural elemenrs, such as asymmetry flowing fabric, perthitic and band structural, melting lineation and intraformational flowing fold were formed. However, the microfabrics features of the rocks are equilibrium textures of triple sides, similar to the metafabrics of rocks by static crystalline metamorphism; the deforrnation of mineral grain is not obvious and the intracrystalline deformation textures did not develop:the metamorphic tectonite of lower crustal tectonic 1evel,the tectonic gneiss,was formed.

Keyword:Daqing Mountain; high-grade metamorphic rock; ductile shear zone; rheomorphic mechanism; tectonic gneiss; metamorphic rock; petrology.

 

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作者简介:刘正宏(1960-),男,教授,主要从事构造地质学与区域地质调查研究.ORCID:0000-0002-1868-4549.E-mail: zhliu@jlu.edu.cn

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