Gangdese arc detritus within the eastern Himalayan Neogene foreland basin:Implications for the Neogene evolution of the Yalu-Brahmaputra River system

摘要

In order to assess the spatial and temporal extent of sediment transport from the Gangdese batholith of Tibetto the eastern Himalayan Neogene foreland basin, we performed U-Pb and Lu-Hf analyses on elevensandstone samples from three locations within the Arunachal and Sikkim Himalaya. We also analyzeddetrital zircons from eight modern river sand samples of the Yalu-Brahmaputra River system and its majortributaries in the eastern Himalaya. Results from the river sands are used to contrast the provenancecharacteristics of the Gangdese arc in southern Tibet with nominally equivalent arc rocks east of theHimalaya in the northernmost Indo-Burma Ranges. Our results indicate that the deposition of Gangdesebatholith-derived sediment within the eastern Himalayan foreland: (1) occurred throughout Late Mioceneand Pliocene time (-10-3 Ma), (2) was limited to the Arunachal Himalaya, and (3) was sourced north of theHimalaya. This detritus may have been deposited by a transverse Himalayan river, such as the Subansiri River,as suggested by high percentages of the Gangdese-derived zircons within the Neogene samples (15-31%) andS- to SW-oriented paleocurrent directions from two of the Neogene sample localities. At this time, ourpreferred model to explain the data invokes capture of an originally westward-flowing Yalu River by theSubansiri River at -10 Ma, followed by capture of the Yalu River by the Siang River at -3-4 Ma.