Zircon U–Pb age, Hf isotope composition, and their constraints on tectonic setting of the Saima alkaling complex in the eastern Liaoning Province

The light-red aegirine nepheline syenite in Liaoning Saima area has a LA-ICP-MS U-Pb age of 225.8 ± 1.9 Ma, and the emplacement age of the Saima alkaline complex is the Late Triassic. Aegirine nepheline syenite shows SiO₂ of 55.87%～60.88%, Na₂O of 0.41%～5.32%, Al₂O₃ of 17.81%～19.53%, K₂O of 9.46%～11.91%, MgO of 0.46%～1.36%, σ43 of 7.54～17.01.The total amount of rare earth elements is higher than 300×10⁻⁶, and it is strongly enriched with light rare earth elements. Depletion of high field strength elements such as Nb, Ta, P, and enrichment of large ion lithophilic elements such as Rb, Th, shows the characteristics of alkaline rich rocks. The zircon ε_Hf (t) value is −13.37 ~ −9.30, the corresponding two-stage Hf model age T_DM2 is 2102~1855 Ma. The Saima alkaline complex may be formed by the partial melting of the lower crust (or upper mantle) under the dynamic background of subduction-squeezing to inland extension and extension conversion. The age of emplacement (225.8 ± 1.9 Ma) may represent the time when the lithosphere began to stretch and thin on the northern margin of the North China Craton, and also the time when the Tanlu fault was formed.