Age and provenance of the Yingou Group in Sunan area of North Qilian Mountain: Evidence from detrital zircon U-Pb Dating

The Yingou Group is mainly distributed in Sunan area of North Qilian orogenic belt and consists of intermediate-basic volcanic rocks, pyroclast intercalated with silicalite, metamorphic mudstones and sandstones. U- Pb ages of detrital zircons from two sandstone samples in the Upper Yingou Group were measured using the LA- ICP- MS method. The ages of the youngest zircons,(425±2) Ma and(425±5) Ma, indicate that the deposition took place in the Early to Middle Silurian. Therefore, the age and the composition of the Yingou Group should be redefined. The concordant ages of detrial zircons show that the provenance in the Upper Yingou Group was derived mainly from the Central Qilian block(800-1000 Ma, 1600-1800 Ma), subordinately from the North Qilian arc and synorogenic granites(425-510 Ma), and rarely from the North China plate(1800 Ma).