SHRIMP zircon ages of the Dagangou volcanic rocks in the Eastern Kunlun orogenic belt and their implications

The Maoniushan Formation of molasse, formed in a post-orogenic environment in Dagangou area of the Eastern Kunlun Mountains, rests unconformably on pre-Devonian strata. Its formation time is critical for determining the terminal of the Caledonian orogeny and the initiation of splitting in the Late Paleozoic. The authors conducted zircon U-Pb dating for volcanic rocks of the Up-per Maoniushan Formation by SHRIMP. The samples(DG01 and DG02) of the Upper Maoniushan Formation yielded two average zircon U-Pb ages of 403.6±5.1Ma and 409±3.4Ma. Combined with the previous studies, the formation time of the Maoniushan For-mation should be Late Silurian-Early Devonian. This provides a constraint on the starting time of splitting in the Late Paleozoic and also means that the Caledonian orogeny ended before the Late Silurian-Early Devonian.