Age dating of alkali granite in Jingesitai area of Dong Ujimqin Banner, Inner Mongolia, and its significance

Abstract：Alkali granites are exposed in Jingesitai area near China-Mongolia border area. The intrusions, which were assigned to Late Hercynian or Indosinian in 1∶200000 regional geological survey, constitute a part of the southern belt alkali granites in the Xingmeng orogenic belt. Alkali granites are characterized by high silica, high alkali, quasi-aluminum and low magnesium and calcium. The content of silica varies from 74.80 % to 78.74%, that of K2O is higher than that of Na2O, and that of alkali is higher than 8%. The REE content is low, the fractionation between LREE and HREE is not very obvious, (La/Yb)N values vary from 0.898 to 5.168 and δEu values are in the range of 0.07-0.89. Therefore, the granites belong to PAG and might have been the product of post-orogeny. U-Pb isotopic age dating of the alkali granite is （284.8±1.1） Ma, implying a product of Early Permian magmatism.