Augen granites from the southern Lancangjiang tectonic zone in western Yunnan: Zircon U-Pb dating and its geological implications

The wide-spread magmatic rocks are developed in the southern Lancangjiang tectonic zone, especially in the Changning-Menglian tectonic zone in western Yunnan as a major suture zone of the Palaeo-Tethyan Ocean. The approaches of the magmatism in this area will be helpful to the better understanding of the evolutionary processes and relevant geodynamic mechanisms of the Palaeo-Tethyan Ocean. In this paper, the authors present the highresolution zircon U-Pb and Sr-Nd dating results for the deformed augen granites from the southern Lancangjiang tectonic zone. Two pieces of augen granite samples 13YJ-45-1 and 13YJ-45-3 and one piece of mylonitized granite sample 13YJ-46 give the respective ages of 213 Ma, 216 Ma and 211 Ma of magmatic crystallization, which should be assigned to the Late Triassic rather than to the Palaeozoic or the Middle Triassic in age. Geochemically, the augen granites have the features of the S-type granites, suggesting that they may be originated from the partial melting of the middle and upper crust metasedimentary rocks, and represent the products generated in the postcollisional-extensional tectonic settings during the late stages of the Palaeo-Tethyan evolution in the Lancangjiang tectonic zone.