Abstract The eastern Himalayan syntaxis, where the Yarlung Tsangpo sharply bends, is one of the areas experiencing most rapid exhumation on Earth. The rapid exhumation is often regarded as the result of capture of the Yarlung Tsangpo by the Brahmaputra River. However, both the timing of integration of the Yarlung Tsangpo-Brahmaputra River and initiation of the rapid syntaxial exhumation are debated. As the ultimate sedimentary trap of the Yarlung Tsangpo-Brahmaputra River, the Nicobar Fan is a window to look into the drainage evolution and exhumation history of the eastern Himalaya. International Ocean Discovery Program Expedition 362 drilled the Nicobar Fan for the first time, recovering fan sediments dating back to the Early Miocene (∼19 Ma). We apply trace elements and Sr-Nd isotopes to investigate the provenance of the sediments in the Nicobar Fan with the aim of constraining the timing of integration of the Yarlung Tsangpo-Brahmaputra River and initiation of the rapid syntaxial exhumation. The geochemical and Sr-Nd isotope compositions indicate an eastern Himalayan source dominated by the Greater Himalaya, with significant Gangdese arc contribution and primarily carried by the Brahmaputra River. Flux of Gangdese arc material appears to have been continuous from the base of the Nicobar Fan, suggesting that the Yarlung Tsangpo-Brahmaputra River has been established at least since ∼19 Ma. Synchronously with the sharp rise in sedimentation rate, the abrupt change of geochemical and isotope compositions at ∼9.2 Ma indicates an increase in erosion of the Greater Himalaya as the result of initiation of rapid exhumation in the broad syntaxial region. The proportion of Greater Himalayan material increased again at 3.5–1.7 Ma, consistent with a younger pulse of rapid exhumation focused in the core of the syntaxis since ∼3.5 Ma. Our results show that initiation of the rapid syntaxial exhumation postdated integration of the Yarlung Tsangpo-Brahmaputra River by at least ∼10 m.y. Therefore, tectonic uplift rather than river capture could be responsible for the initiation of the rapid syntaxial exhumation.

中文翻译：

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喜马拉雅东部的排水演化和挖掘历史：来自印度洋东北部尼科巴扇的见解

摘要 雅鲁藏布江陡弯处的喜马拉雅东部构造构造是地球上剥蚀速度最快的地区之一。快速的挖掘通常被认为是雅鲁藏布江被雅鲁藏布江捕获的结果。然而，雅鲁藏布江-雅鲁藏布江合并的时间和快速构造剥落的开始都存在争议。作为雅鲁藏布江-雅鲁藏布江最终沉积圈闭，尼科巴扇是了解喜马拉雅东部流域演化和折返历史的窗口。国际海洋发现计划探险队 362 首次钻探了尼科巴扇，恢复了可追溯到早中新世（~19 Ma）的扇沉积物。我们应用微量元素和 Sr-Nd 同位素研究尼科巴扇沉积物的来源，目的是限制雅鲁藏布江-雅鲁藏布江整合的时间和快速句法折返的开始。地球化学和 Sr-Nd 同位素组成表明喜马拉雅东部源以大喜马拉雅山为主，冈底斯弧贡献显着，主要由雅鲁藏布江携带。冈底斯弧物质的通量似乎从尼科巴扇的底部开始是连续的，这表明雅鲁藏布江-雅鲁藏布江至少自约 19 Ma 以来已经建立。与沉积速率的急剧上升同步，地球化学和同位素组成在～9. 2 Ma 表明大喜马拉雅山的侵蚀增加，这是由于广泛的句法区域开始快速剥脱的结果。大喜马拉雅山物质的比例在 3.5-1.7 Ma 时再次增加，这与自 3.5 Ma 以来集中在构造构造核心的较年轻的快速剥脱脉冲一致。我们的研究结果表明，雅鲁藏布江-雅鲁藏布江与雅鲁藏布江-雅鲁藏布江整合至少约10米后，快速构造剥脱的开始。因此，构造隆升而不是河流捕获可能是导致快速构造剥脱的原因。