Abstract: The monzogranite in the Jiazishan of Inner Mongolia is located in the middle part of the Daxing’anling Mountains. To determine its intrusive age and tectonic environment, the geochronology and petrogeochemistry of the monzogranite have been systematically studied. The results show that the zircon U-Pb age of the monzogranite is (302.9±1.2) Ma, which is the product of Late Carboniferous magmatism. The monzogranite is characterized by high silica (w (SiO2)=74.73%-76.60%), rich alkali (w (Na2O+K2O)=6.20%-7.03%) and high aluminum saturation index (A/CNK=1.43-1.58), belonging to the high-K calc-alkaline series. Rb, K, Th and U are enriched, while Ba, Sr, Ti, Nb and P are obviously V-shaped depleted. The REE pattern shows a right-leaning enrichment type of LREE, with negative Eu anomaly (δEu=0.46- 0.67). The high differentiation index (ID) (88.89-91.55) and low solidification index (IS) (1.68-4.78) indicate that the monzogranite has undergone the evolution of high differentiation and is a type highly differentiation I-type granite with a tendency to evolve to A-type granite. The 176Hf/177Hf value is 0.282 850-0.282 951, the εHf (t) value is 9.2-12.5, and the two-stage mode age (TDM2) is 910-603 Ma, suggesting that the monzogranite may be the product of partial melting of juvenile crust in Neoproterozoic. The monzogranite in the Jiazishan area of Inner Mongolia was formed in the post-orogenic stage, and its formation may be related to the transformation of the tectonic setting from extrusion to post-collisional extension after the closure of the Paleo-Asian Ocean.

Key words: zircon U-Pb dating, geochemistry, Late Carboniferous, post-orogenic tectonic setting, Paleo-Asian Ocean, Xing-Meng orogenic belt, Jiazishan area, Inner Mongolia