U-Pb dating of the detrital zircons from the Lancang Group Complex in western Yunnan and its geological significance

Although numerous previous studies, no direct evidences of geological ages are recorded for the Lancang Group Complex in western Yunnan. The U-Pb age data of the detrital zircons in sericite quartz schist from the Lancang Group Complex in the Changputang-Datianshan zone have provided convincing evidence for the formation age of the Lancang Group Complex. The cathodoluminescence (CL) images show that these zircon crystals generally display the well-defined oscillatory zonation and suggest a magmatic origin of the zircons. The age data for the detrital zircons in the sericite quartz schist sample PM08-B1 range between 452 and 3016 Ma, with the youngest age group of 452 ±26 Ma, implying that the maximum depositional age of the Lancang Group Complex is less than 452 ±26 Ma. One zircon grain with a U-Pb age of 255 ±3Ma exhibits a slight cathodoluminescence image and has no internal structures, which is characteristic of a type of metamorphic recrystallization zircons and in general aggrement with the previous data. In general, the Lancang Group Complex is dated at a depositional age of less than 452 ±26 Ma, The U-Pb age (255 ±3 Ma) of the metamorphic crystalline zircons reveals that the metamorphic events once took place during the Late Permian.