Abstract: Geological field investigation, facies analysis and detrital zircon U-Pb geochronology were used to study the so-called ‘Langxian Cretaceous mélange (KL), which outcrops on the southern side of the eastern Yarlung Zangbo suture zone in Shannan Prefecture, southern Tibet. The results obtained indicate that the southern ‘KL’ is quite similar to the Upper Triassic flysch Langjiexue Group in lithofacies, provenance and relative probability of detrital zircons U-Pb age (distinctive ca. 230Ma and 530Ma in age population), but different from the narrow belt of the northern counterpart. It is suggested that most of the ‘KL’ can be assigned to the Langjiexue Group, implying that the collision boundary between Indian and Eurasian continents is the Naidong-Jindong-Moluo fault (Zhanang-Jiacha-Nang-Milin zone), rather than the Zedang-Jiacha-Langlagangze fault in the north or Naidong-Qusong-Bailu fault in the south.