LA-ICP-MS zircon U-Pb dating of Devonian Sangejing Formation and Dundunshan Group in Hongliuyuan, Beishan area, Gansu Province

Based on a study of LA-ICP-MS zircon U-Pb dating of basic volcanic rocks from lower Sangejing Formation and andesitic volcanic rocks from middle Dundunshan Group in Hongliuyuan of Beishan area, Gansu Province, this paper reveals that volcano-sedimentary rocks of Sangejing Formation were formed at 420 ± 15Ma, corresponding to Late Silurian, and volcanic rocks of Dundunshan Group were formed at 367 ± 9.5Ma, equivalent to Late Devonian. These data indicate that Beishan ocean basin was at the stage of the subduction-disappearance in Late Silurian, and entered into the collisional orogeny period, whereas the Dundunshan volcanic rocks were produced by rift extension and entered into a new phase, i.e., Late Paleozoic intraplate extension.