Detrial zircon LA-ICP-MS U-Pb ages of the Devonian Shujiaba Group in Shujiaba area of the West Qinling tectonic zone: Constraints on material source and sedimentary age

Choosing the Shujiaba Group detrital rocks in Shujiaba area as the study object and using LA-ICP-MS zircon U-Pb isotope chronology, the authors studied the sedimentary age and material source of the Shujiaba Group. 413Ma, the mean of the minimum ages group, indicates that the sedimentary age of Shujiaba Group should be the Middle Devonian. Four groups can be recognized from the zircon ages spectrum: Sinian-Early Paleozoic age group (619~409Ma), with the peak value of 445Ma；Neoproterozoic age group (930~735Ma), with the peak value of 849Ma; Mesoproterozoic age group (1760~1033Ma); and Paleoproterozoic-Neoarchaen age group (3095~2478Ma). The age group information indicates that the material sources were mainly derived from North Qilian orogenic belt，the northern margin of West Qinling tectonic zone and the basement of North China block, of which the North Qilian orogenic belt and the northern margin of West Qinling tectonic zone made the major contribution, with the last one playing the leading role. The material source features and regional geology suggest that the Shujiaba Group was formed in a rifted basin resulting from the transitional tectonic setting from syn-collision (compressional setting) to post-collision (extensional setting).