内蒙古东乌珠穆沁旗京格斯台碱性花岗岩年龄及意义
Age dating of alkali granite in Jingesitai area of Dong Ujimqin Banner, Inner Mongolia, and its significance
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摘要: 提要：东乌珠穆沁旗京格斯台碱性花岗岩出露于中蒙边界附近的京格斯台地区，1∶20万区域地质调查归之于华力西晚期（Kγ43(2)）和印支期（γ15）侵入体，是兴蒙造山带南带碱性花岗岩的一部分。该岩石具高硅、富碱、准铝、贫镁钙的特点，SiO2含量为74.80%~78.74%，K2O＞Na2O，全碱含量大于8.0%，属于过碱性和碱性花岗岩类（PAG）。岩石稀土总量偏低，轻重稀土元素分馏程度不明显，（La/Yb）N值0.898.84~5.168，δEu为0.07~0.89，铕强烈亏损。为后造山伸展环境下的产物。采用单颗粒锆石U-Pb同位素稀释法测定京格斯台碱性花岗岩的年龄，206Pb/238U表面年龄加权平均值为（284.8±1.1）Ma，为早二叠世岩浆活动的产物。
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关键词:
- 碱性花岗岩 /
- A型 /
- 后造山 /
- 锆石U-Pb年龄 /
- 东乌珠穆沁旗京格斯台
Abstract: 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. -
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