Detrital zircon U–Pb age and provenance analysis of Dacaotan Formation in the Qiagai area of theWwest Qinling orogenic belt

[Objective] There are many disputes about the the age and prowenance of Dacaotan Formation. It is beneficial to the stratigraphic division and mineral resources investigation to clarify these problems.[Methods] With clastic rocks of the Upper Devonian Dacaotan Formation at Qiagai area in the West Qinling Orogenic belt as the study object, the authors used LA-ICP-MS zircon U-Pb isotope geochronological method to explore the age and prowenance of Dacaotan Formation.[Results]The results show that the detrital zircon ages can be divided into 4 groups:(1)The Archen-Paleoproterzoic (2232-3258Ma); (2)The Mesoproterzoic (1018-1791Ma); (3) The Neoproterzoic (544-999Ma); (4)The Early Paleozoic(417-519Ma). Among which, the Early Paleozoic(417-519Ma) ages data possess the largest proportion, accounting for about 39.6% of the total data. The lesser is the Neoproterzoic(544-999Ma) ages, about 37.3%. The other two groups ages possess a smaller proportion.[Conclusions] Analysis show that, the provenance source of Dacaotan Formation were much more complicated and characterized by obvious diversity and periods, derived from northern margin of western Qinling orogenic belt, the eastern part of the Qilian orogenic belt and the basement of North China plate. The predominant part among them was the active magmatic arc produced by collision orogen, which come from the northern margin of western Qinling orogenic belt and Qilian orogenic belt during the Caledonian period.