Detrital zircon evidence from Burma for reorganization of the eastern Himalayan river system

For studying the sedimentary source to sink relation and reorganizing of the mountain rivers around eastern Himalayas, we conducted a detrital zircon study from the Irrawaddy and Inner-Burma Basin by combined SHRIMP U-Pb dating and in-situ Hf isotope measurements. These results, together with U-Pb and Hf isotope data of igneous zircons from the eastern Transhimalayan batholith from southern Tibet to Burma, allow a more quantitative examination of the source provenance of sediments deposited in the drainage since Miocene time. For example, among 47 out of 62 dated zircons from Upper Miocene sandstone that show Cretaceous to Paleogene 206Pb/238U ages, 24 grains have positive ɛHf(T) values up to +16. Whilst zircons of such ages are common in the Transhimalayan plutons, those showing high ɛHf(T) values have been observed so far only in the Gangdese batholith. Our results, therefore, support the notion that by Late Miocene time the Yarlu Tsangpo, which flows past the Gangdese batholith in southeastern Tibet, drained into the Irrawaddy River. We attribute this river routing to not only regional topographic control but also the dextral movement of the Jiali-Gaoligong-Sagaing fault system that appears most active during the Middle Miocene. Subsequent reorganization of these mountain rivers was affiliated with headward erosion of the Brahmaputra River that eventually cut across the Namche Barwa Syntaxis and captured the Yarlu Tsangpo drainage to form the modern eastern Himalayan river system.