Zircon U-Pb chronology and Lu-Hf isotopic characteristics of the Pre-Sinian Wumaqing Formation and its intrusions in Yakou area, Miyi County, Sichuan Province, and their geological significance

There are several sets of metasedimentary rock series distributed intermittently in the western margin of Yangtze Block, it is of great significance to determine the ages of different rock units in the area for discussing the tectonic evolution. This study has conducted zircon LA-ICP-MS U-Pb dating and Lu-Hf isotopic analysis of the metasedimentary rocks from the Wumaqing Formation as well as its intrusive gneissose biotite adamellite in Yakou area, western margin of Yangtze Block. The results indicate that the sedimentary age of Wumaqing Formation in the area is between 1. 19 similar to 1. 01Ga, and the strata belongs to Huili Group rather than Kangding Group. The "Lengzhuguan Formation" under the Wumaqing Formation is not a metasedimentary stratum but a set of gneissose biotite adamellite. The detrital zircon dating of the Wumaqing Formation have two main peaks of similar to 1. 56Ga and similar to 2. 50Ga, five minor peaks of similar to 1. 43Ga, similar to 1. 68Ga, similar to 1. 87Ga, similar to 2. 32Ga and similar to 2. 68Ga, it is speculated that its sedimentary material sources are mainly from Cuoke complex, buried or undiscovered Archean basement, contemporaneous magmatic rocks and the recycled of early metasedimentary rocks in the southwestern margin of Yangtze Block. The epsilon(Hf) (t) values of detrital zircons has changed significantly at similar to 1. 7Ga, suggesting that the tectonic regime in the western margin of Yangtze Block has shifted from continental crust convergence to rift activities, and the rift magmatism has peaked at similar to 1. 56Ga. The positive epsilon(Hf) (t) values of granitic pluton implies that there was a new continental crust growth event at similar to 1. 0 Ga in the western margin of Yangtze Block, possibly is the product of rift magmatism under the extensional collapse tectonic setting after the Grenvillian Orogeny.