东北帕米尔中新世中下地壳物质的折返过程:公格尔西滑脱剪切带的构造变形与年代学证据

Exhumation of the Miocene Mid-Lower Crust Material in Northeast Pamir:Structural Deformation and Geochronological Evidence from the West Kongur Detachment

公格尔西滑脱剪切带位于东北帕米尔公格尔片麻岩穹窿西缘。通过我们详细的野外观测、显微构造观察、石英电子背散射衍射（EBSD）测试以及锆石U—Pb测年，对公格尔西滑脱剪切带的几何学、运动学特征及其形成演化时限进行了研究。公格尔西滑脱剪切带糜棱岩中大量的石榴子石、矽线石和蓝晶石等表明其为高级变质产物。S／C组构、旋转碎斑及不对称褶皱等变形现象说明剪切带上盘向W或SW低角度剪切的运动特征。高级变质糜棱岩和浅色岩脉记录约20Ma的^205U-^238Pb锆石年龄，说明公格尔西滑脱剪切带初始形成于早中新世。结合前人研究成果，我们认为公格尔西滑脱剪切带曾是狭长的帕米尔中下地壳滑脱带的最北段。由于新生代印度亚洲大陆碰撞以后印度板块仍持续向N俯冲推进，帕米尔地壳由S向N开始增厚，进变质作用最初发生于南帕米尔，约20Ma时到达北帕米尔。东北帕米尔中下地壳物质开始折返于中新世中期。而直到6～4Ma，东北帕米尔公格尔地区开始快速隆起，此时公格尔新生代高级变质岩才快速折返。

The West Kongur Detachment （WKD） is located in the w estern margin of the Kongur gneiss dome in northeast Pamir. Based on the detailed field investigation, microstructure observation, quartz EBSD testing and zircon U-Pb dating, this study analyzed the geometry, kinematics and evolution time of the WKD. The presence of garnet, sillimanite and kynite in the mylonites from the WKD indicates that the shear zone moved from mid-lower crust to the surface. S/C fabric, rotating porphyroclasts and asymmetric folds in the WKD indicate the characteristic of W- or SW-dipping shearing movement of the hanging wall of the shearing zone. High-grade metamorphic mylonites and leucosomes records the zircon 206U-238Pb age of 20 Ma, suggesting that the WKD initially formed at early Miocene. Combined with previous studies, it can be concluded that the WKD should be the northernmost segment of Cenozoic Pamir mid-lower crust. Due to the fact that the Indian plate continued to northward thrusting after the Cenozoic Indian-Asian collision and this led to thickening of the Pamir crust from south to north, prograde metamorphism firstly occurred in south Pamir in the Eocene, and reached northern Pamir -20 Ma later. The exhumation of Mid-Lower crust materials in northeastern Pamir started in middle Miocene. It was not until 6 - 4 Ma when the Kongur region started to uplift rapidly and the Cenozoic metamorphic rocks exhumed quickly.