内蒙古苏尼特左旗地区阿木乌岩体LA-ICP-MS锆石U-Pb年龄及其地球化学特征

LA-ICP-MS zircon U-Pb ages and geochemical characteristics of Amuwu pluton in Sonid Zuoqi area,Inner Mongolia

对苏尼特左旗地区阿木乌岩体进行LA-ICP-MS锆石U-Pb测年、主量元素、稀土元素和微量元素测试分析。结果表明,岩体成岩年龄为235.1±3.2 Ma,属中三叠世。岩体具有高SiO2、富K2O、低CaO、低TiO2的特征。强烈亏损Sr、Ba、Ti、P等元素,富集K、Rb、Th等亲石元素,具有右倾"海鸥型"球粒陨石标准化稀土配分型式及强烈的负铕异常等特点。A/CNK=0.77～1.19,A/NK=1.26～1.64,表明阿木乌岩体具有偏铝质A型花岗岩的特征。具有较高的Y/Nb值(2.31～3.00>1.2),显示出A2型花岗岩的特征,说明岩体形成于造山后的伸展环境。

The zircon U-Pb ages and geochemical characteristics of Amuwu pluton in Sonid Zuoqi area were determined by the method of LA-ICP-MS zircon U-Pb dating as well as major,trace and REE elements analysis.The results showed that the 206pb/238U age was 235.1 ±3.2 Ma,formed in Middle Triassic.The granite was characterized by high SiO2 and K2O,low CaO and TiO2,strongly depleted in Sr,Ba,Ti,P,and enriched in K,Rb,Th.The pluton showed particularly intensive Eu negative anomalies and with a seagull shape to rightward in chondrite-normalized REE pattern.The A/CNK and A/NK values were 0.77 ～ 1.193 and 1.26 ～ 1.64,respectively,belonging to A-type granite.According to the high Y/Nb value （2.31 ～3.00 ＞ 1.2）,the pluton shows the characteristics of granite type A2,which formed in the extensional environment of post-orogenic.