Zircon U-Pb age and geochemistry of Late Triassic intrusive rocks in Qinghe area, eastern Liaoning Province and its indication to the tectonic evolution of the eastern North China Craton

Monzodiorite and monzogranite are developed in Qinghe area of Liaodong Peninsula, which is located in the east of North China Craton.We have carried out systematic LA-ICP-MS zircon U-Pb dating and geochemistry of the two types of intrusive rocks to explore the magmatic emplacement mechanism and tectonic background of Qinghe area of Liaodong Peninsula in the Late Triassic.The weighted average zircon U-Pb ages of monzodiorite and monzogranite are 212 ±2 Ma and 221 ±2 Ma, respectively.According to geochemical analysis, monzodiorite has medium SiO₂ content(50.44%~55.18%, with an average of 52.20%), high MgO(3.18%~6.2%, with an average of 5.20%), TFe₂O₃(7.83%~8.85%, with an average of 8.37%)and total alkali(7.04%~8.00%, with an average of 7.50%), indicating that the monzodiorite in Qinghe area belongs to quasi aluminous shoshonite series.The rocks are enriched with large ion lithophile elements(LILE), relatively deficient in high field strength elements(HFSE), medium Nd/Th(3.70~9.75, average 5.83)and Rb/Sr(0.07~0.12, average 0.09)ratios, and high Nb/U(9.11~13.2, average 10.8)ratios, indicating that they are mainly composed of crust derived materials and a small amount of mantle derived materials.Monzogranite is rich in SiO₂(76.10%~76.80%, with an average of 77.12%), poor in MgO and TFe₂O₃.Its magmatic composition is mainly composed of siliceous and aluminous components in the crust, belonging to peraluminous Ⅰ-type granite.At the same time, it is deficient in high field strength elements Nb, Ta, P and Ti, and the Nd/Th(0.62~1.73, average 1.23)ratios are close to the value of crust source rock, suggesting that the original magma should be a partial melting of continental crust materials.Through the analysis of petrology, geochronology, geochemistry and tectonic environment, combined with the study of regional tectonic evolution of Liaodong Peninsula, it is considered that the monzodiorite is the result of deep subduction of the Yangtze craton and post extension of the North China craton, and the monzogranite is in the syn-collision and compression environment.