大兴安岭环二库地区新元古代晚期花岗岩发现及其地质意义

DISCOVERY AND GEOLOGICAL SIGNIFICANCE OF THE LATE NEOPROTEROZOIC GRANITE IN HUANERKU, DAXINGANLING REGION

摘要: 最近的研究成果表明，在大兴安岭新林-喜桂图旗断裂东段的吉峰、嘎仙、环二库地区存在一些蛇绿岩岩石组合.在大兴安岭地区大扬气林场环二库蛇绿混杂岩中的花岗岩中获得锆石LA-ICP-MS U-Pb年龄为557.2±2.2 Ma，表明其形成于新元古代晚期.岩石总体上具略贫碱，弱过铝质钙碱性，具有不明显的Eu负异常，为弱过铝钙碱性I型花岗岩.岩石富集轻稀土元素和Hf、Ba、Nd、U等元素，相对亏损Th、Nb、Ta、Zr等元素.结合新元古代末期新林-吉峰地区存在新元古代洋盆，认为该岩体可能形成于该大洋俯冲环境.

Abstract: The latest research shows that the assemblage of ophiolite is developed in Jifeng, Gaxian and Huanerku areas along the eastern part of Xinlin-Xiguituqi fault in Daxinganling Mountains. Based on the study, the LA-ICP-MS zircon U-Pb age of 557.2±2.2 Ma is obtained from the granite in the ophiolitic melange in Huanerku area, indicating it was formed in Neoproterozoic period. The rock is generally characterized by slightly poor alkali, weakly peraluminous calc-alkaline with indistinct negative Eu anomaly, enrichment of LREEs and Hf, Ba, Nd and U, and relative depletion of Th, Nb, Ta and Zr, belonging to weak peraluminous calc-alkaline I-type granite. Considering the existence of Neoproterozoic ocean basin in Xinlin-Jifeng area, it is concluded that the granite is possibly the product of ocean subduction.