内蒙古大青山深层次韧性剪切带的特征及其成因机制  

THE CHARACTERS AND GENESIS OF THE LOWERCRUST DAQINGSHAN DUCTILE SHEAR ZONES IN THE INNER MONGOLIA

作　　者：陈晓锋[1] 刘正宏[1] 徐仲元[1] 赵庆英[1] 吴新伟[1] 

机构地区：[1]吉林大学地球科学学院,吉林长春130061

出　　处：《矿物岩石》2008年第1期48-53,共6页Mineralogy and Petrology

基　　金：国家自然科学基金(40572117)

摘　　要：内蒙古大青山高级变质杂岩区发育多条近东西向、平行相间排列的深层次韧性剪切带。其主要位于不同岩性的边界,以发育各种条带构造及S—C组构为特征。韧性剪切带与其间弱变形域的应变强弱相间,连续变化的特点可用变形分解理论合理解释。剪切带中的构造岩具有明显不同于中浅层次糜棱岩的微观组构特征,主要表现为无残斑基质之分,广泛发育复晶石英条带,长石多呈三边平衡结构等,反映了地壳深层次的变形主要受扩散蠕变及熔体强化的颗粒流动机制控制。同构造矿物组合与石榴石-黑云母矿物对温压计(710℃,0.6 GPa)显示变形环境为高角闪岩相-麻粒岩相。同构造岩体单颗粒锆石U-Pb同位素年龄在1 900 Ma^2 200 Ma之间,推测剪切带大致形成于早元古代。韧性剪切带的构造形迹暗示其形成于斜向挤压(NNE-SSW)的构造环境,结合年代学资料及当时的大地构造环境,可认为其是阴山陆块与鄂尔多斯陆块斜向(NNE-SSW)水平会聚导致应变分解的产物。Some lower-crust ductile shear zones （DSZ） occurred in Daqingshan area of Inner Mongolia. The DSZ lie mainly at the boundaries of different lithology, charactered by well developed, steeply-dipping banding and S-C fabrics. The alternating distribution of high strain zones and low strain zones in the DSZ may be reasonably explained by deformation partitioning. Microstructural study showed that the characters of tectonic gneiss of lower crust DSZ were obviously different from those of mylonites developed in the middle crust. The tectonic gneiss of the lower crust was characterized by well developed banding foliation without porphyroclasts or matrix, which may be resulted from partial melting of rock. Meanwhile, feldspar grains in the gneiss touch each other with triple point configuration, suggesting that the rock deformation mechanism in lower crust was controlled mainly by diffusion creep and granular flow strengthened by melt. Garnet-biotite geothermobarometry analysis revealed a high amphibolite-granulite metamorphic facies with a deformation temperature of 710 ℃ and a confining pressure of 0.6 GPa. The 1 900 Ma-2 200 Ma age obtained by single zircon isotopic dating from the intrusive body in the gneiss demonstrated that the DSZ was formed in the early Proterozoic period. It was considered that the DSZ was resulted from the horizontal convergence of Yinshan land mass and Eerduosi land mass in a NNE-SSW direction.

关 键 词：韧性剪切带 构造形迹 变形分解 构造片麻岩 斜向水平会聚 大青山 

分 类 号：P542.2[天文地球—构造地质学]