帕隆藏布江中游地壳剥露特征

Crust erosion characteristics in the middle reach of the Purlung Tsangpo River

为揭示东喜马拉雅构造结演化过程,也为未来可能重大工程建设提供基础地质资料,对帕隆藏布江中游9块基岩样品进行了黑云母^(40)Ar/^(39)Ar测年,并利用“Pecube”软件对该地区的地壳剥露速率进行半定量计算。样品黑云母^(40)Ar/^(39)Ar年龄范围为103~12.5 Ma,对应地壳剥露速率范围为0.068~0.50 km/Ma。帕隆藏布江流域地壳剥露速率具有明显的东西差异特征,下游(西段)地壳剥露速率显著高于中游(东段)。年龄数据及其模拟计算结果表明,相对于东喜马拉雅构造结内部,帕隆藏布江中游流域地壳剥露活动较弱且较稳定。雅鲁藏布江对帕隆藏布江的袭夺,使得帕隆藏布下游(西段)重新进入河流演化幼年阶段,河流快速下切剥蚀可能是导致该地区地壳剥露速率东西差异的原因。

To reveal the tectonic evolution process of the eastern Himalayan syntaxis and provide basic geological data for probable significant engineering construction,this study reports 9 biotite ^(40)Ar/^(39)Ar ages in the middle reach of the Purlung Tsangpo River and semiquantitatively calculates the rock erosion rates represented by these ages using the modeling code"Pecube".The measured biotite ^(40)Ar/^(39)Ar ages range from 103-12.5 Ma,corresponding to erosion rates ranging from 0.068-0.5 km/Ma.The rock erosion rates of the Purlung Tsangpo River have obvious differences between the western and eastern sections,which are characterized by the downstream section(western section)being significantly higher than that of the middle section(eastern section).Ages and simulation results show that in contrast to the eastern Himalayan syntaxis,the crust erosion rate in the middle reach of the Purlung Tsangpo River is lower and stable.The Purlung Tsangpo River was captured by the Yarlung Tsangpo River,which allowed the Purlung Tsangpo River downstream(western section)to change into a youth stage of fluvial geomorphological evolution again.The rapid river incised likely resulted in the erosion rate differences between the western and eastern sections.