大兴安岭北段索图罕地区碱长花岗岩成因及形成构造背景

本文对大兴安岭北段索图罕地区碱长花岗岩进行了系统的全岩地球化学、锆石U-Pb同位素年代学的研究，并探讨了其成因和构造意义。LA-ICP-MS锆石U-Pb定年结果表明，花岗岩形成于早白垩世，年龄为（139.50±0.56）Ma。岩石地球化学结果显示，索图罕林场碱长花岗岩属于高钾钙碱性的A型花岗岩，岩石具有富硅和碱、贫CaO和MgO的特征，岩石稀土元素质量分数较高，相对富集轻稀土元素，具有明显的负Eu异常，富集Rb、Th、U、K等大离子亲石元素，亏损Nb、P、Ti等高场强元素，稀土元素配分图解具有右斜"V"字形的特征。索图罕林场碱长花岗岩为弱过铝质A型花岗岩，来源于地壳物质的部分熔融。样品微量元素构造判别图解落入后碰撞区域，代表伸展环境。结合区域地质特征，认为该碱长花岗岩的形成与蒙古-鄂霍茨克洋闭合后的岩石圈伸展相关。

Petrogenesis and Tectonic Setting of Moyite in Suotuhan Area,Northern Great Xing'an Range

In this research, the whole-rock geochemistry and zircon U-Pb isotope chronology of moyite from Suotuhan area in the northern Great Xing'an Range are studied and their petrogenesis and tectonic significance are discussed. The LA-ICP-MS zircon U-Pb dating shows that the moyite formed in the Early Cretaceous with the ages of (139.50±0.56) Ma. The geochemical characteristics suggest that the Suotuhan moyite belongs to high K calcalkaline A type granite, and it is featured by high content of SiO₂ and alkaline, and low content of CaO and MgO. The moyite has high rare earth elements (REE), and is relatively rich in LREEs with distinct negative Eu anomalies in chondrite-normalized REE diagram, which is characterized by right oblique and ‘V’-shape. The Suotuhan alkali feldspar granite is a weakly peraluminous A-type granite derived from partial melting of crustal material. The regional geological characteristics indicate that the formation of the moyite was related to lithospheric extension caused by closure of the Mongol-Okhotsk Ocean.