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作 者:蒋孝君 彭云彪 董晓杰[2] 李华明 涂颖 Jiang Xiaojun;Peng Yunbiao;Dong Xiaojie;Li Huaming;Tu Ying(No.208 Geological Party,CNNC,Baotou 014000,China;College of Earth Sciences,Jilin University,Changchun 130061,China)
机构地区:[1]核工业二〇八大队,内蒙古包头014000 [2]吉林大学地球科学学院,吉林长春130061
出 处:《地球科学》2021年第9期3057-3073,共17页Earth Science
基 金:中国核工业地质局铀矿勘查项目(Nos.2018⁃15,202004⁃1).
摘 要:为了解蒙古‒鄂霍次克构造体系的远程作用及其在中国东北以南的影响范围,在内蒙古多伦火山盆地羊盘沟地区开展了流纹斑岩锆石U-Pb同位素年代学、岩石地球化学及区域对比研究.结果显示,其形成时代为144.2±0.6 Ma,属于早白垩世早期.主量元素SiO_(2)含量为73.25%~76.72%,K2O含量为4.64%~7.87%,K_(2)O/Na_(2)O值在1.15~3.82之间,A/CNK值为0.79~0.99;副矿物为磁铁矿、锆石和磷灰石等,属准铝质高钾钙碱性‒钾玄岩系列A2型流纹岩类;稀土元素总量高(320.76×10^(-6)~415.70×10^(-6)),富集轻稀土元素、大离子亲石元素K和Rb、高场强元素Zr和Hf以及元素U、Th等,亏损重稀土元素、大离子亲石元素Ba和Sr、高场强元素Nb和Ta以及元素P、Ti等,显著Eu负异常(δEu=0.08~0.15).表明流纹斑岩形成于后碰撞构造环境,是早白垩世蒙古‒鄂霍次克洋闭合后某个伸展事件下的产物,因此,蒙古‒鄂霍次克构造体系在中国的影响范围向东南至少延伸至蒙东南‒冀北一带,且对应的蒙古‒鄂霍次克洋东段的闭合完成时间应早于144.2 Ma.In order to understand the long-range function of the Mongolian-Okhotsk tectonic system and its influence range to the south in China.Zircon U-Pb isotopic geochronology,rock geochemistry and regional correlation of rhyolite porphyry were carried out in yangpangou area,Duolun volcanic basin,Inner Mongolia.Zircon LA-ICP-MS U-Pb isotopic dating shows that the age of its formation is 144.2±0.6 Ma,belonging to the early Early Cretaceous.The content of SiO_(2) is 73.25%-76.72%,K_(2)O is 4.64%-7.87%,K_(2)O/Na_(2)O is 1.15-3.82,and A/CNK is 0.79-0.99.The accessory minerals are mainly magnetite,zircon and apatite.It belongs to the type A2 rhyolite of the quasi aluminous high potassium Ca-alkaline shoshonite series.The total amount of rare-earth elements is high(320.76×10^(-6)-415.70×10^(-6)).Light rare-earth elements,large ion lithophile elements K,Rb and high field strength elements U,Th,Zr and Hf are enriched.Heavy rare-earth elements,large ion lithophile elements Ba,Sr and high field strength elements P,Ti,Nb,Ta are deficient.Eu negative abnormality is significant(δEu=0.08-0.15).The above characteristics indicate that the rhyolite porphyry was formed in the background of post-collision,reflecting the postcollisional extension event after the closure of Mongolia-Okhotsk Ocean in Early Cretaceous.Therefore,the influence range of the Mongolia-Okhotsk tectonic system in China extends to the southeast at least to the southeast of Inner Mongolia to the north of Hebei,and the completion time of the corresponding Mongolia-Okhotsk Ocean east section should be earlier than 144.2 Ma.
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