内蒙古阿尔塔拉中三叠世A型花岗岩锆石U-Pb年龄、地球化学特征及构造意义

在内蒙古二连-贺根山缝合带新发现西乌旗阿尔塔拉A型花岗岩，岩性为二长花岗岩。锆石LA-ICP-MS U-Pb测年结果显示，该二长花岗岩的侵位年龄为242.9±1.5Ma，形成时代为中三叠世。阿尔塔拉A型花岗岩地球化学特征为高钾钙碱性系列，具有较高的SiO2（75.89%~76.79%）、K2O（4.18%~4.30%）和Na2O+K2O（8.23%~8.57%），贫CaO、MgO、Sr、Ba、Eu、Ti和P，相对富集Ga、Rb和Th。该岩石稀土元素配分曲线为海鸥式，具有显著的负Eu异常（δEu=0.11~0.14）。在地球化学判别图解上，阿尔塔拉A型花岗岩显示A2型后造山花岗岩特征，其形成于后造山伸展环境。结合二连-贺根山缝合带蛇绿岩、岛弧型-后造山型岩浆岩的时空演化关系，古亚洲洋二连-贺根山洋盆可能在二叠纪晚期闭合，并在三叠纪进入后造山伸展构造演化时期。

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.