内蒙古杭嘎勒晚二叠世石英二长闪长岩地球化学特征与锆石U-Pb测龄

Geochemical characteristics and LA-ICP-MS zircon U-Pb dating of Late Permian quartz monzodiorite in Hanggale,Inner Mongolia,China

通过野外观测、岩相学及全岩地球化学数据分析,结果表明内蒙古阿拉善右旗杭嘎勒晚二叠世石英二长闪长岩主体岩石与包体的稀土元素特征一致,轻重稀土分馏程度强烈,具弱的负铕异常,稀土配分曲线为向右倾,属轻稀土富集型。石英二长闪长岩显示了I型花岗岩的特点。包体与主体岩石同时具有表现出元素Ce、Nd、Zr富集,而Nb、Sr、P、Ti亏损,显示形成于增生在大陆边缘正常弧花岗岩的特征。AR-SiO2图解显示,主体与包体岩石虽同属钙碱性+拉斑玄武系列区,显示了同源岩浆演化的特点,在R1-R2图解上,大部分样品集中在碰撞前与碰撞后花岗岩区分界处,以碰撞前为主;在Nb-Y图解上,样品落在了火山弧-同碰撞花岗岩区;在Rb-(Y+Nb)图解上,样品落在了火山弧花岗岩区,反映石英二长闪长岩形成于板块边缘的岩浆弧环境。LA-ICP-MS锆石U-Pb年龄测定,表明主体岩石年龄为(251.9±2.7)Ma。杭嘎勒晚二叠世石英二长闪长岩为碰撞前火山弧花岗岩,研究区在晚二叠世时属于活动大陆边缘的火山弧。

The field observation, petrography and geochemical data of the Late Permian quartz monzodiorite show that the REE features of in the Hanggale area of Alax Right Banner are consistent with its pluton. The Enrichment of LREE and the weak negative Eu anomalies show the characteristics of an I-type granite.The depletion of Nb,Sr,P,Ti elements indicates the features of an arc granite accreting on the continental margin.In the R 1-R 2 diagram,most of the samples are concentrated along the boundary between the pre-collision granite and the post-collision granite area. In the Nb-Y diagram,the samples fall into the area of the volcanic arc and the syn-collisional granite. In the Rb-（Y＋Nb）diagram,the samples exit in the area of volcanic arc granite.LA-ICP-MS zircon U-Pb dating shows that the age of the main rock body is 251.9±2.7 Ma.The quartz monzodiorite of Hanggale is a pre-collisional volcanic arc granite,and the Hanggale area was a volcanic arc belonging to the active continental margin in Late Permian.