西藏冈底斯中段南缘叶巴岩群膝折构造及其地质意义

位于冈底斯南缘的叶巴岩群内发育着复杂的构造变形，是典型的构造转换带，已有证据表明这些复杂的构造变形与发育在叶巴岩群中的驱龙、甲玛等大型矿床的形成密切相关，其中大量发育的膝折构造是脆-韧性转换构造带中的代表。此次研究工作的主要对象为叶巴岩群内部的膝折构造，研究其分布特征、变形及扩容方式，分析其运动学特征及温度环境，结合构造变形时代探究其形成的大地构造背景。绿泥石温度计及方解石e双晶特征实验结果显示研究区膝折构造形成温度环境在170~299℃之间，表明研究区膝折构造形成的过程伴随着构造抬升。根据宏观露头及显微视域对于膝折构造的运动学特征分析，判断主压应力方向为自上而下（铅直向下），这一以垂向挤压的重力为主的主应力方向与该时期的冈底斯南缘大规模南北向滑覆构造的主压应力一致，研究结果认为发育于叶巴岩群内部的浅部膝折构造为25 Ma以来南拉萨地体伸展滑覆构造背景之下的变形作用的产物。 

The kinks of the Yeba Group in the southern margin of the central Gangdese of Tibet and its geological significance

The Yeba Group, located in the southern margin of Gangdese, is a typical structural transition zone with complex multistage structural deformations. Previous evidence has shown that these complex structural deformations are related to the Qulong and Jiama deposits developed in the Yeba Group. Kinks therein are a representative of structural deformation in the brittle-ductile structural transition zone. Their deformation and distribution characteristics, kinematic features and temperature environment are the focus of this study, so as to explore the tectonic background. The results from the chlorite thermometer and calcite e-twins characteristics show that the temperature is between 170℃~299℃ for the formation of the kinks in the study area, indicating a tectonic uplift during the formation process. According to the kinematic analysis of the kinks based on field outcrops and BSE-based images, it is inferred that the principal compressive stress is top-down (vertically downward), which is consistent with the principal compressive stress of the large-scale NS-trending gliding nappes in the southern margin of Gangdese during that period. Combined with the results of the relative chronological analysis, we believe that the kinks developed in the Yeba Group are the product of brittle-ductile deformation under the extension of the southern Lhasa terrane since 25 Ma.