内蒙古海拉斯图乌拉A型花岗岩年代学、地球化学特征及其构造意义

内蒙古苏尼特左旗查干敖包镇南部紧邻中蒙边境线海拉斯图乌拉一带发育的一套钠铁闪石霓辉石碱性花岗岩,是二连—贺根山构造带的重要组成部分,通过对其进行年代学、地球化学研究,以探讨区域构造演化。锆石LA-ICP-MS U-Pb同位素年龄测试结果显示该岩体的侵位年龄为(285.4±1.1) Ma,属早二叠世。岩石地球化学研究表明该岩石具高硅、富碱、准铝、贫镁钙的特点,其化学成分SiO₂含量为76.12%~80.10%,Na₂O+K₂O含量为7.62%~9.19%,MgO含量为0.06%~0.10%,CaO含量为0.11%~0.20%,碱性指数(K₂O+Na₂O)/Al₂O₃=0.98~1.04,属于碱性岩系,岩石稀土总量偏低,轻、重稀土元素分馏明显,δEu 为0.37~0.51,Eu强烈亏损,属造山后伸展事件的产物。其成因可能和华北板块与西伯利亚板块对接后的伸展作用有关,指示二连—贺根山构造带在早二叠世可能已进入造山后演化阶段。

Geochronology,Geochemistry, and Tectonic Significance of the Hailasituowula A-type Granites in Sunitezuoqi,Inner Mongolia

The Hailasituwula arfvedsonite-aegitite augite-alkali granite is distributed in southern Chagan’aobao, Sunitezuoqi of Inner Mongolia, an important component of the Erlian-Hegenshan tectonic belt. Through chronological and geochemical studies on it, to explore regional tectonic evolution, LA-ICP-MS zircon U-Pb dating yielded (285.4±1.1) Ma, belonging to the Early Permian, This geochemical study shows that the rocks are featured by being metaluminous, and have relatively high SiO₂(76.12%-80.10%) and alkalis (K₂O+Na₂O=7.62%-9.19%), but low MgO (0.06%-0.10%) and CaO (0.11%-0.20%). The Alkaline index (AI) is 0.98-1.04, and the rocks belong to the alkaline series. The total REE contents of the rocks are relatively low, and the LREEs and HREEs are obviously fractionated. Negative Eu anomalies are distinct (δEu=0.37-0.51), which are coeval with the regional post-orogenic extension. The results indicate that the Erlian-Hegenshan tectonic belt may have entered the post-orogenic stage in the Early Permian.