蒙古-鄂霍次克洋的远程作用:来自内蒙古东南部羊盘沟地区流纹斑岩成因的证据

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SiO₂含量为73.25%~76.72%，K₂O含量为4.64%~7.87%，K₂O/Na₂O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. 

The Remote Role of Mongolia-Okhotsk Ocean:Evidences from the Origin of Rhyolite Porphyry in Yangpangou Area,the Southeast of Inner Mongolia

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 SiO₂ is 73.25%-76.72%, K₂O is 4.64%-7.87%, K₂O/Na₂O 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 post-collisional 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.