内蒙古乌日尼图花岗岩的年代学、地球化学及其地质意义

乌日尼图隐伏岩体位于内蒙古自治区苏尼特左旗查干敖包镇西北乌日尼图地区，主要岩石类型为细粒-中细粒花岗岩、二长花岗岩。岩相学及地球化学特征研究表明，乌日尼图花岗岩体属于高钾钙碱性岩系，SiO₂含量为74.85%～78.10%，K₂O/Na₂O比值介于1.45～3.08之间，铝指数A/CNK=1.00～1.21，属过铝质岩石。主微量稀土元素分析表明，该岩体富集Rb、Th、U等元素而Ba、Nb、Sr、P和Ti强烈亏损，Eu为负异常(δEu= 0.22～0.39)，总体呈现轻稀土富集的右倾“V”形分布配分模式。LA-ICP-MS锆石U-Pb定年表明，乌日尼图花岗岩体形成于早白垩世(139 Ma)，为燕山运动晚期的产物。乌日尼图花岗岩体属A型花岗岩，形成于伸展的大地构造环境，且源区成分不均一，源岩可能主要由富黏土的泥质岩夹杂少量砂屑岩变质形成。

Geochronology and Geochemistry of the Wurinitu Granites in Inner Mongolia and Their Geological Implications

The Wurinitu granitoid pluton, located in the northwestern of the Wurinitu Village, Chaganaobao town, Sunidzuoqi County, Inner Mongolia, is a concealed rock mass and mainly composed of fine to middle-fine grained granite and adamellite. Petrography and geochemical characteristics indicate that it belongs to high-K calc-alkaline series. Its SiO₂ contents range from 74.85% to 78.10%, while K₂O/Na₂O ratios and A/CNK values vary from 1.45 to 3.08 and 1.00 to 1.21, supposed to a suite of peraluminous rock. Rb, Th and U elements are enriched in the intrusion while Ba, Nb, Sr, P and Ti depleted. REEs show characteristics of obvious negative Eu anomalies(δEu= 0.22-0.39)and right-dipping“V”patterns with LREE enrichment. On the basis of LA-ICP-MS U-Pb chronological study of zircons, the U-Pb dating results from the granites are 139 Ma implying that they formed in Early Cretaceous, Late Yanshanian stage. Chemically, the granitoids belong to A-type, implying that they formed under an extensional tectonic setting. The source compositions of the granites are different, and they are mainly derived from clay-rich pelite with a spot of arenite, resulted from metamorphism.