摘要:雅鲁藏布江缝合带是新特提斯洋俯冲消亡的残余，记录了新特提斯洋打开—闭合的全过程。本文以雅鲁藏布江缝合带西段仲巴地区南侧的纳久混杂岩为研究对象，进行了详细的放射虫年代学，砂岩碎屑锆石U-Pb同位素年代学以及碎屑组分统计研究。我们的数据表明，纳久混杂岩中硅质岩含有大量保存较好的放射虫化石，包含Pseudodictyomitra carpatica带典型分子，根据放射虫时代组合确定其时代为早Barremian阶；混杂岩中砂岩岩块主要为岩屑砂岩，不同样品碎屑锆石得出的最大沉积年龄介于95～73 Ma之间。碎屑锆石U-Pb年龄源区分析表明，碎屑物质来自北侧的冈底斯岩浆弧和拉萨地体。纳久混杂岩南侧的砂岩沉积时代为早白垩世，碎屑锆石U-Pb年龄源区表明具有典型的特提斯喜马拉雅特征。我们的数据表明，纳久混杂岩基质时代为早白垩世，砂岩岩块时代为晚白垩世，与北侧的早白垩世蛇绿岩共同组成了白垩纪的增生楔，随着印度与欧亚大陆的碰撞仰冲到特提斯喜马拉雅之上。
关键词: 物源分析/
碎屑锆石U-Pb年代学/
放射虫/
海沟沉积/
新特提斯洋俯冲
Abstract:The Yarlung Zangbo suture zone records the opening and closing history of the Neo-Tethys Ocean. In this paper, we presented new radiolarian chronology, sandstone petrology and detrital zircon U-Pb data from the Najiu mélange within the Yarlung-Zangbo suture zone in the south of the Zhongba area. Our data indicated that the chert matrix in the Najiu melange contain well preserved Early Barremian radiolarian fossils, including Pseudodictyomitra carpatica with typical molecules. The sandstone blocks in the mélange are mainly lithic sandstones, and the maximum deposition age obtained from detrital zircon lie in the range of 95～73 Ma. Provenance analysis of the detrital zircon age showed that the sediments was derived from the Gangdese arc. The coherent quartz sandstone on the south side of the Najiu melange is Early Cretaceous in age, and the detrital zircon U-Pb provenance is typical of Tethys Himalayan affinity. Our data show that the Early Cretaceous chert matrix and late Cretaceous sandstone block constitutes the Cretaceous accretionary wedge and was obducted over the Tethyan Himalaya during India-Asia collision.
Key words:Provenance analysis/
Detrital zircon/
U-Pb chronology/
Radiolaria/
Trench deposition
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