嫩江-八里罕断裂带岭下韧性剪切带变形特征

The Characteristics of Structural Deformation for the Lingxia Ductile shear zone of Nenjing-Balihan Fault Belt in Northeastern China

嫩江-八里罕断裂带位于东北地区中部、大兴安岭的东缘，为松辽盆地的西缘控盆断裂。断裂带传统认识上被认为是一条NNE向的深大断裂，其性质为正断层或拆离断层。笔者野外地质考察过程中，在断裂带中南段吉林省白城市岭下地区发现韧性剪切带，通过对该韧性剪切带构造要素系统测量和统计、显微构造观察、有限应变测量、石英组构EBSD（电子背散射衍射）分析和古应力值测量，明确了岭下剪切带变形程度为初糜棱岩-糜棱岩、石英组构以低温底面组构为主，滑移系为{0001}，变形温度在400℃左右的变形特征，并初步认为嫩江一八里罕断裂带曾经历左旋走滑变形阶段；结合断裂带相关年代学资料，确定走滑时间为早白垩世中期（134～113Ma），其形成机制与西太平洋伊泽纳崎板块向欧亚大陆俯冲的运动与NWW向NNW转向有关。

As the west boundary fault of Songliao basin and the eastern margin of the Greater Hing＇an Mountains, Nenjiang- Balihan fault belt is located in the central part of Northeastern China. Nenjiang-Balihan fault belt is considered traditionally to be a huge deep-seated fault with NNE-striking, and it is characterized by a normal fault or detachment fault. During field work, the authors found a ductile shear zone in Lingxia area, the middle of the fault belt. By the measurement of structural elements, the micro-structure studies, the finite strain measurement, the studying of crystal preferred orientations of quartz determined by EBSD （electron back scatter diffraction） and the measurement of the dynamically recrystallized quartz grain size,the authors calculated the paleo-stresses for the deformation rocks in the ductile shear zone, it shows that the feature of Lingxia ductile shear zone is sinistral strikeslip, develops protomylonite - mylonite with ca. 400℃ deformation temperature, and quartz fabrics is mainly low temperature bottom surface fabrics with slip system of {0001}. Based on the previous achievements about the features and formation date, Neijiang- Balihan fault belt have experienced a sinistral strike-slip ductile shearing fault in middle Early Cretaceous （134 - 113 Ma）, and the dynamic tectonic setting of the Nenjiang - Balihan are related to moving direction changing from NWW to NNW of the Western Pacific Izanagi plate obliquely subducting under the Eurasia plate.