SHRIMP Zircon U-Pb dating of Bangmu admellite in Luxi, western Yunnan, and its tectonic implications

Abstract：SHRIMP zircon U-Pb dating of the Bangmu admellite in Luxi of western Yunnan Province was carried out in order to determine the age and discuss the tectonic environment of the granite. The results show that the zircons from the granite have clear oscillatory zones，their Th／U ratio is between 0.13 and 1.00, and their weighted average 206Pb/238U age is (120.5 ± 1.7) Ma(n=15,MSWD = 1.6), suggesting that the crystallization age of the Bangmu admellite is Early Cenozoic. Geochemistry of the granite shows that it is of the Al-supersaturated type and belongs to typical strongly peraluminous I-granite. The Rb-(Yb+Ta) and Rb-(Nb+Yb) diagrams of the granite indicate that the granite was formed in a valconi arc granite (VAG) setting. With the features of the valconi arc magmatic activity, the granite is the product of partially melted crust in a geological condition of crustal thickening resulting from the subduction and collision between the Zogang-Baoshan continental massif and Bomi-Tengchong massif along Bangong Lake-Nujiang-Linshui-Ruili suture zone from northeast to southwest during the Late Jurassic and Early Cretaceous period. The granite was formed in the valconi arc period and the compressional environment. The determination of the Bangmu admellite’s crystallization provides new evidence for the Paleozoic tectonic evolution of the Tengchong massif．