Detrital zircon LA-ICP-MS U-Pb ages of the Paleogene Leidashu Formation in Huili, Sichuan Province and their geological significance

Based on LA-ICP-MS U-Pb dating method, the authors made the U-Th-Pb isotopic measurement of the detrital zircons from the Paleogene Leidashu Formation in Huili area, the south part of the Sichuan Basin. 72 groups of effective single grained zircon U-Pb ages were obtained, and the U-Pb age spectrum was set up in this paper. The results show that the detrital zircon ages are in the range of 2465~204Ma, suggesting a period between the most early Early Paleoproterozoic Siderian period and the most late Late Triassic Rhaetian stage. The age distribution has a strong episodic style with five concentrated ranges and five distinct peak values, and the main provenances were the western margin of the Yangtze Block and the “Sanjiang” orogenic belt on the western side. The detrital zircon U-Pb age spectrum of the Leidashu Formation reveals that the western margin of the Yangtze Block has experienced five important tectonic thermal events, i.e., the crust accretion in the Paleoproterozoic, the Rodinia Supper Continent assemblage in the Mesoproterozoic, the Rodinia Supper Continent breakup in the late Neoproterozoic, the basalt eruption in the Permian and the Indosinian movement in the Late Triassic, evidently corresponding with the evolution of the western margin of the Yangtze Block. A comparison with the detrital zircon U-Pb age spectrum of the Paleogene Liujia Formation in the north part of the Sichuan Basin shows that the detrital zircon U-Pb age spectrum of the Leidashu Formation is characterized by the lack of Jurassic and Cretaceous signals and the addition of Early Ordovician and Early Devonian signals, indicating that the provenance of the north part of the Sichuan Basin and that of the south part of the Sichuan Basin show some difference. Detrital zircon U-Pb age spectrum similarity comparison shows that the detrital zircon U-Pb age spectrum of the Leidashu Formation has relatively high precision and that the Yangtze Craton and Cathaysian Continent have had tight affinity since 1000Ma, whereas the affinity between the Yangtze Craton and the North China Craton began to be established at 400Ma.