内蒙古阿拉善右旗杭嘎勒中二叠世石英闪长岩地球化学特征和LA-ICP-MS锆石U-Pb定年

Geochemical Characteristics and LA-ICP-MS Zircon U-Pb Dating of the Middle Permian Quartz Diorite in Hanggale,Alax Right Banner,Inner Mongolia

杭嘎勒地区中二叠世石英闪长岩,轻重稀土分馏程度较强,无明显铕异常,稀土配分曲线为向右倾,属轻稀土富集型。中二叠世石英闪长岩显示了I型花岗岩的特点。中二叠世石英闪长岩表现出元素Th、Ta、Sr、Hf元素富集,而Nb、La、P元素亏损。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,反映石英闪长岩形成于板块边缘的岩浆弧环境。LA-ICP-MS锆石U-Pb定年表明主体岩石年龄(266.4±3.7)Ma。杭嘎勒晚二叠世花岗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。

Quartz diorites in Hanggale area are characterized by strong REE fractionation, enrichment of LREE, and without significant Eu anomalies, implying an I-type granite. Enrichment of Th, Ta, Sr, Hf elements and depletion of Nb, Sr, P, Ti elements. In the R1-R2 diagram, most of the samples are concentrated in the pre-collision granite area. In the Nb-Y diagram, the samples fall into the area of the volcanic arc- syncollisional granite. In the Rb-（Yq-Nb）diagram, the samples lie in the area of volcanic arc granite. LA- ICP-MS zircon U-Pb dating shows that its age is 266.4 ±3.7Ma. The Middle Permian quartz diorite of Hanggale was a pre-collisional volcanic arc granite, and Hanggale area was a volcanic arc that belonged to active continental margin in Middle Permian.