Chronology and geochemistry of the granitoids in Heri Town, Tongde County, Qinghai Province, and its tectonic significance

In this study, the author used LA-ICP-MS zircon U-Pb isotopic dating method and obtained weighted average zircon U-Pb age of 229.7±1.0 Ma from the biotite granodiorite in Heri Town, Tongde County, Qinghai Province.The geochemical characteristics show that it belongs to high-K calcium-alkali series, and resulted from partial melting of crustal components, with weak negative Eu anomalies and right-inclined chondrite-normalized REE patterns.Based on a comprehensive analysis of previous researched, the authors hold that the biotite granodiorite was formed in the Late Triassic, and belonged to I-type granite formed in the active continental margin environment before the plane collision.Its genesis was closely related to the northward subduction of the Ańyemagen-Mianlue Ocean.The results obtained by the authors provide a new age constraint for the entrance of West Qinling into the syn-collision stage in the Indosinian.