桐柏-大别南缘殷店-马垅韧性剪切带的变形及年代学分析

殷店-马垅（简称殷马）韧性剪切带是桐柏-大别造山带南缘的一条重要的边界断裂，对其精细的构造变形研究将有助于进一步认识桐柏-大别造山带的演化方式和过程。本文主要对殷店和马垅两个地区进行了详细的剖面观测，利用有限应变测量，计算出殷马剪切带中岩石应变椭球长短轴的平均轴率为1.69，靠近剪切带的岩石应变量大，向北远离剪切带，应变量减小；通过构造应力场分析查明剪切带的古应力状态，最大压应力σ₁为北北东-南南西向，对应最大拉应力σ₃为北西西-南东东向。岩石的有限应变分析和应力场状态，反映出板块间的碰撞挤压作用力在平行剪切带和垂直剪切带方向上存在应力分解。剪切带内糜棱岩中的锆石U-Pb定年结果显示，其年龄为172～137 Ma，据此得出殷马剪切活动时代主要为中侏罗世-早白垩世。

Deformation analysis and chronological dating of Yindian-Malong ductile shear zone in the southern margin of Tongbai-Dabie orogenic belt

Yindian-Malong(Yin-Ma for short)ductile shear zone is an important boundary fault in the southern Tongbai-Dabie orogenic belt. The fine study of its structural deformation will be helpful to further understand the way of evolution and process of the Tongbai-Dabie orogenic belt. In this paper, the detailed field work was carried out in the Yindian and Malong area. The strain ellipsoid axial mean rate of 1.69 of the rocks in the Yin-Ma shear zone is calculated by the finite strain measurement, and the strain intensity decreased with the distance from the center of the shear zone. The analysis of the tectonic stress field find out the shear stress state that the maximum compressive stress σ₁ is in the NNE-SSW direction, corresponding to the maximum tensile stress σ₃ is in the NWW-SEE direction. The results of rock finite strain and stress field shows that the collision-generated extrusion force decomposed the components parallel to and perpendicular to the shear zone. Zircon U-Pb ages of mylonite in the shear zone are in the age distribution of 172～137 Ma which suggests the Yin-Ma shear zone activity epoch is mainly in Middle Jurassic to Early Cretaceous, to the end of Yanshanian period.