摘要
北大坂花岗岩体位于北祁连中东段,为了精确测定岩体形成年代,对岩体中的浅灰黑色中粗粒英云闪长岩锆石进行了阴极发光(CL)成像观察,并利用LA-MC-ICP-MS对锆石进行微区U-Pb同位素测年。锆石的加权平均年龄为(447. 2±2. 4) Ma,表明其属于晚奥陶世岩浆活动产物。岩石地球化学数据分析表明,浅灰黑色中粗粒英云闪长岩为准铝质-弱过铝质高钾钙碱性花岗岩,富集大离子亲石元素,亏损高场强元素,稀土元素配分曲线呈右倾型,轻、重稀土元素分馏较为明显,显示出了I型花岗岩的特征。样品在构造判别图上均落入后碰撞花岗岩区域,结合区域上其它花岗岩体形成的构造环境研究,反映了北大坂岩体形成于北祁连洋壳的北向俯冲作用导致的北祁连岛弧与阿拉善地块碰撞期结束后的构造环境,暗示着北祁连洋在奥陶世晚期已经闭合。
The Baidaban granite locates in mid-east of Northern Qinlian. In order to determine the exact formation age of the granite,cathodoluminescence( CL) imaging and LA-MC-ICP-MS Zircon U-Pb for the granite were carried out. TheU-Pb dating of these zircon yidlded a weighted mean age of( 447. 2 ± 2. 4) Ma. Geochemical data show that granodiorite is a aluminous graniteand belongs to the high-K calc-alkaline series. It is characterized by enrichment of LILE and depletion of HFSE,with REE patterns exhibiting the right-deviation type and strong fractionation with LREE enrichment. These show that the granites have characteristics of I-typegranite. These features suggest that the granodiorite has the characteristics of post-collisional granite. Combine the tectonic environment of granite body in adjacent region,the Baidaban granite body formed in a collision tectonic setting of the North Qilian island arc colliding with the Alaxa massif,which may be induced by the northward subduction of the North Qilian ocean crust. It implied that the North Qilian ocean was closed in Late Qrdovician.
作者
陈云杰
杨昆
武彬
赵如意
王刚
苟学明
CHEN Yun-jie;YANG Kun;WU Bin;ZHAO Ru-yi;WANG Gang;GOU Xue-min(Research Institute NO. 203 of Nuclear Industry, Xianyang 712000, China;Key Laboratory of Metallogeny and Mineral Resource Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences,Beijing 100037 , China)
出处
《东华理工大学学报（自然科学版）》
CAS
2019年第2期108-115,共8页
Journal of East China University of Technology(Natural Science)
基金
中国地质调查局项目(DD2016013622)
中国核工业地质局铀矿项目(201803)
