The Qinling and Qilian orogenic belts have been separated by the the Xinyang-Yuanlong ductile shear zone. The relationship between the Qinling and Qilian orogenic belts remained disputed, because the tectonic lineation of the both orogens is at an oblique angle to each other. Longshan complex is located in the tectonic conjunction of the Qinling and Qilian orogens, consistsing of middle to high grade metamorphic assemblages. It still remained controversial about the formation age and tectonic settings. In this study, detrital zircons collected from the biotite quartz schist of the Longshan complex have been dated by the LA-ICP-MS, yielding 4 age ranges including two major age populations of 1 097～795 Ma（49%, age peak at ～929 Ma）and 2 713～2 265 Ma（22%, age peak at ～2 435 Ma）, and two minor age populations of 575～471 Ma（12%, age peak at ～541 Ma）and 1 864～1 539 Ma（14%, age peak at ～1 717 Ma）. Confined by the youngest peak age and the oldest intrusion age of the Longshan complex, the meta-sediments were deposited between the Early Cambrian and the Early Ordovician. Therefore, the meta-sediments was formed obviously later than the Late Archean-Paleoproterozoic TTG rocks of the Longshan complex, indicating that the meta-sediments are not ourcrops of the Archean-Paleoproterozoic basements along southern margin of the North China Block（NCB）. Compared with the characteristic age peaks of the surrounding tectonic terrains, the age populations of detrital zircons, ranging from the Archean to Paleoproterozoic（2 713～2 265 Ma）and from the Late Paleoproterozoic to Early Mesoproterozoic（1 864～1 539 Ma）, are thought to be derived from the southern margin of the NCB. The age population of detrital zircons ranging from the Early to Middle Neoproterozoic（1 097～795 Ma）is mainly derived from the North Qinling orogenic belt and central Qilian block, while that ranging from the Late Neoproterozoic to Early Paleozoic（575～471 Ma）are derived from the Wushan-Tianshui tectonic belt. Therefore, the biotite quartz schist from the Longshan complex is derived from the southern margin of the NCB in the north as well as the Qilian-Qinling orogenic belt in the south, indicating that the meta-sediments deposited in a rifting or extending Hongtubu back-arc basin during the Early Paleozoic period, which is similar to the tectonic environment of those parametamorphic rocks from the Kuanping complex and Erlangping complex in the eastern North Qinling orogenic belt.
Xu Kexin He Yanhong Chen Liang Meng Xiangshu Wu Lei. Studies on the detrital zircon U-Pb dating of the Longshan complex in the tectonic conjunction of the Qinling-Qilian orogen: Provenance and tectonic setting[J]. Chinese Journal of Geology, 2018, 53(3): 1054-1074.