西藏冈底斯带扎雪-门巴韧性变形带形成时代及构造背景

The ages and tectonic setting of the Zaxoi-Mamba ductile shear zone in the Gangdise orogenic belt, Xizang

关键词:  扎雪-门巴韧性剪切带  ⁴⁰Ar/³⁹Ar年龄  构造背景  西藏

Key words:  Zaxoi-Mamba ductile shear zone  ⁴⁰Ar/³⁹Ar age  tectonic setting  Xizang

摘要:

扎雪-门巴韧性变形带位于冈底斯构造带中部,是一条由北而南的逆冲推覆兼具右行走滑的斜冲韧性剪切带。带内所形成的构造岩主要为构造片麻岩和糜棱岩类,对花岗质糜棱岩中的黑云母进行⁴⁰Ar/³⁹Ar年龄测试,获得105.2±1.7M a,认为该韧性剪切带形成于早白垩世。岩石组合和显微构造特征表明该韧性剪切带形成于中绿片岩相到高绿片岩相环境,可能与班公湖-怒江弧后洋盆的闭合碰撞有关。

Abstract:

The Zaxoi-Mamba ductile shear zone lies in the middle part of the Gangdise orogenic belt, and occurs as an overthrusted and right-lateral strike-slip oblique ductile shear zone. The tectonites in this zone include tectonic gneiss and mylonite. The biotite from the granitic mylonite gives a ⁴⁰Ar/³⁹Ar age of 105.2 ±1.7 Ma, implying that the ductile shear zone may be traced back to the Early Cretaceous. The petrological associations and microstructures have disclosed that the ductile shear zone was formed in the medium to high greenschist facies conditions, and may be associated with the closure and collision of the Bangong Lake-Nujiang back-arc oceanic basin.