Zircon U-Pb dating, geochemistry and tectonic implications of the Artala Middle Triassic A-type granite in Inner Mongolia

The newly recognized Artala A-type granite occurs along the Erenhot-Hegenshan suture in Xi Ujimqin Banner of Inner Mongolia and is composed of monzogranite.LA-ICP-MS zircon U-Pb dating yielded a weighted average age of 242.9±1.5Ma.The age suggests that the granite was emplaced in the Middle Triassic.The granite belongs to high-K Calc-alkaline series, and is characterized by rich SiO₂(75.89%~76.79%) and K₂O(4.18%~4.30%), high alkali(Na₂O+K₂O=8.23%~8.57%), low CaO, MgO, Sr, Ba, Eu, Ti, P, and relatively high Ga, Rb and Th. In addition, it has lower total rare earth element (REE) content with obviously negative Eu anomalies(δEu=0.11~0.14), showing a typical flat gull-wing shaped REE distribution pattern.The Artala monzogranite exhibits the typical geochemical characteristics of A-type granites. According to the chemical subdivision diagrams of the A-type granitoids, the Artala A-type granite belongs to A-type granitoid, which was formed and emplaced in a post-collisional extension setting. Based on the previous studies of the time-space evolution of the ophiolites, arc granitoids, and post-collisional granitoids in the Erenhot-Hegenshan suture, the authors suggest that the Erenhot-Hegenshan oceanic basin of the Paleo-Asian Ocean was probably closed at the end of the Permian and that the Erenhot-Hegenshan suture entered the post-collisional extension tectonic evolution period in Triassic.