Provenance of the Tapo Formationin Lueyang Area: Evidence from Detrital Zircons LA-ICP-MS U-Pb Geochronology

The Tapo Formation,located to the south of the Mianlue Tectonic Zone,is one of the main sedimentary stratas of the Late Paleozoic Lueyang Basin.It is characterized by a set of terrigenous clastic rocks, mainly including conglomerate, pebbly sandstone,sandstone and siltstone (siltyslate).This paper conducted the LA-ICP-MS U-Pb dating on the clastic rock from Tapo Formation and analyzed its forming environment and provenance characteristics combined with the composition of gravels.The combination of lithology,sedimentary structure and highly concentrated age data indicate that the Tapo Formation is near-source accumulation. A large quantity of limestones and dolomite gravels in the Tapo Formation may come from Sinian Doushantuo Formation and Dengying Formation in adjacent area.The available detrital zircon ages are divided into 2 groups:2 089~1 967 Ma and 2 706~2 413 Ma. The age group of 2 089~1 967 Ma accounts for 52% of the total, with a peak at 2.0 Ga; the age group of 2 706~2 413 Ma accounts for 32% of the total, with a peak at 2.46 Ga.Boththe two groups coincide with the geochronological framework of the Yangtze plate. Combined with the tectonic evolution process and related age information of Mianlue Tectonic Zone and the northwestern margin of the Yangtze plate,it is suggested that the adjacent Sinian Doushantuo and Dengying Formation,the Yudongzi Complex and the unexposed Paleoproterozoic basement in the vicinity were the main source areas of the Tapo Formation.The extension of Mianlue Tectonic Zone could continue until Early-Middle Devonian.