The ductile decollement shear zones are in Zhongba microterrane which lies between southern subbelt and northern subbelt in the western part of the Yarlung Zangbo suture zone.The determination of the activity time about the high strain tectonic belt can not only provide constraints for its formation evolution but also provide the important corroborative evidence for the India-Eurasia collision.The samples of muscovite and biotite mylonitic rock were collected from the different parts of deformation in the shear zone to analyze the chronology with the mica 40Ar-39Ar dating.The tested ages including 53.39±0.57Ma,39.45±0.42Ma and 29.41± 0.32Ma in three groups indicate that the shear zone has multi-period tectonic activities.Group one which represents the initial stage of the India-Eurasia collision is the age limit of the shear zone (minimum age).Thus the initial time of plate collision should be the end of the Late Cretaceous to the Early Eocene before 53.39±0.57Ma because the shear zone was the product of the initial collision.Group two which is the cooling age of muscovite that formed under the SN-trending shearing compressive stress represents the period of main collisions.Group three which is the biotite age that formed after the reslip of the shear zone slip at low temperature uplifting stage represents the period of post-collision.%仲巴微地体夹持于雅江缝合带西段分支的南、北亚带之间,地体内发育韧性滑脱型剪切带.对该类高应变构造带活动时间进行厘定,不仅可以为其形成演化提供制约,而且也可为印度-欧亚板块碰撞过程提供重要的年代学佐证信息.在该剪切带不同变形部位采集了含白云母、黑云母糜棱质岩样品,进行云母类单矿物40Ar-39Ar测年.获取年龄数据3组:53.39±0.57Ma、39.45±0.42Ma、29.41±0.32Ma,表明该剪切带具有多期次构造活动叠加特征.其中第1组年龄代表在印度-欧亚板块初始碰撞阶段,剪切带形成的时代下限(最小年龄),因该剪切带是两大板块初始碰撞的产物,所以可佐证板块起始碰撞时间为53.39±0.57Ma之前的晚白垩世末—始新世初期;第2组年龄代表在板块主碰撞阶段,发生继承性的近南北向挤压剪切作用后白云母的冷却年龄;第3组年龄代表了后碰撞阶段,剪切带的再次滑动后低温隆升时期的黑云母年龄.
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