新疆哈尔里克山口门子韧性剪切带变形期次及年代学研究

Geochronology and Deformation Stages of Koumenzi Ductile Shear Zone in Harlik Mountain,Xinjiang

新疆哈尔里克山口门子韧性剪切带作为东天山地区重要的构造记录之一,其变形期次及年代学研究对认识博格达?哈尔里克山乃至整个东天山的区域构造演化具有重要意义。本文基于宏观与微观变形特征、变形温压条件、同位素年代学研究,厘定了两期(脆)?韧性变形,分别是早期韧性逆冲变形和晚期左旋脆?韧性走滑变形。卷入早期韧性逆冲变形的花岗岩、火山岩年代学分析表明,该期变形发生于440.1±3.2 Ma之后;未卷入该期变形的花岗闪长岩脉和辉绿岩脉年代学分析表明,早期韧性逆冲变形发生于298.1±1.0 Ma之前。结合泥盆纪?早石炭世哈尔里克山地区呈现为稳定构造环境以及存在早、晚石炭世地层间的角度不整合,推断早期韧性逆冲变形形成于早、晚石炭世之交,与石炭纪陆内裂谷的闭合有关。晚期左旋脆?韧性走滑变形叠加使早期糜棱岩面理发生褶皱,结合前人获得的259±1 Ma的变质绢云母^40Ar-^39Ar年龄,认为该期变形是晚二叠世受西伯利亚板块向南推挤的陆内转换压缩变形产物。

The Koumenzi ductile shear zone in the Harlik Mountain,Xinjiang,is one of the most significant geological records of tectonic evolution of the East Tianshan.The deformation histories and geochronological results of this shear zone are critical for understanding the regional tectonic evolution of the Bogda-Harlik Mountains,as well as the East Tianshan as a whole.Two stages of ductile to brittle-ductile deformation are identified based on field and micro structure features,temperature and pressure conditions of the deformed rocks,and isotope chronology.The stable tectonic state of the Harlik Mountain from the Devonian to early Carboniferous,as well as the angular unconformity between the upper and the lower Carboniferous strata,the early stage ductile deformation probably took place during the early to late Carboniferous,correlated with the closure of Carboniferous continental rift.Geochronological dating showed that the early stage thrusting ductile deformation occurred no early than 440.1±3.2 Ma,but before 298.1±1.0 Ma,as was constrained by dating results of the deformed granite and volcanic rock and the undeformed granodiorite and diabase veins.The late stage sinistral ductile shearing superimposed on the first stage deformation and folded the early stage mylonite foliation.According to the syn-metamorphism sericite ^40Ar-^39Ar age of 259±1 Ma previously reported,we suggest that the second stage deformation was correlated to the intracontinental transpressive deformation driven by the southward pushing of the Siberian Plate during the Late Permian.