LA-ICP-MS zircon U-Pb dating of the Early Silurian clastic rocks in Dacaotan of Jiayuguan, North Qilian orogenic belt

The detrital rocks distributed in Dacaotan, northern Jiayuguan in the North Qilian orogenic belt were chosen as the study object, which was originally considered to be of the Yingou Group of Middle-Lower Ordovician. LA-ICP-MS zircon U-Pb iso-tope chronology was investigated to study the formation age, material source composition and tectonic background of the Yingou Group. The results show that the sedimentary age of the Yingou Group is earlier than 432.5Ma, and hence its age should be Early Si-lurian and it does not belong to the Yingou Group of Middle-Lower Ordovician. The zircon age spectrum can be evidently divided into four groups:Early Paleozoic age group from 434~521Ma, with the peak value being 447Ma; Neoproterozoic age group from 791~992Ma, with the peak value being 966Ma; Mesoproterozoic age group from 1017~1755Ma, with the peak value varying from 1120Ma, 1278Ma, 1427Ma to 1648Ma; Paleoproterozoic-Neoarchaean age group from 1879~2663Ma, with the peak value varying from 2089Ma, 2428Ma to 2543Ma. Comprehensive analyses show that the material source was derived form Qilian tectonic zone and Alashan block. The Early Paleozoic island-type magmatic rock in Qilian tectonic zone, Neoproterozoic magmatic rock and tectonic zone crystalline basement rock series contributed much to the sedimentation of the detrital rocks.