大兴安岭北段巴升河岩体锆石U-Pb年代学及其地质意义

ZIRCON U-Pb GEOCHRONOLOGY OF BASHENGHE PLUTON IN NORTHERN DAXINGANLING MOUNTAINS: Geological Implications

摘要: 大兴安岭北段扎兰屯地区巴升河岩体由碱长花岗岩组成.采用LA-ICP-MS方法对碱长花岗岩开展锆石U-Pb测年，结果为297.8±3.6 Ma，岩体形成于早二叠世.该岩体4个样品的全岩地球化学等特征显示：巴升河岩体中碱长花岗岩具有富Si、高K、富碱的特征，属于弱过铝质钾玄岩系列，同时，样品∑REE偏高，Eu负异常明显，富集大离子亲石元素，具有A型花岗岩特征，综合前人研究成果及同位素年代学特征，认为兴安地块与松嫩地块拼合的时间早于298 Ma.

Abstract: The Bashenghe pluton in Zhalantun area of northern Daxinganling Mountains is composed of alkali-feldspar granite. The zircon LA-ICP-MS U-Pb dating yields the weighted mean age of 297.8±3.6 Ma, indicating the pluton was formed in the Early Permian. The whole rock geochemistry of 4 samples shows that the alkali-feldspar granite is characterized by rich Si, high K and rich alkali, belonging to weak peraluminous shoshonite series. The characteristics of high ∑REE, obvious negative Eu anomalies and enrichment of LILEs are properties of A-type granite. Combined with previous research results and isotopic chronology, it is concluded that the convergence of Xing'an massif and Songnen massif occurred before 298 Ma.