大兴安岭北部凤凰山地区英云闪长岩地球化学特征与锆石U-Pb定年

Geochemistry and Zircon U-Pb Dating of the Tonalite from Fenghuangshan Area in Northern Daxing'anling

凤凰山地区位于大兴安岭北部额尔古纳地块和兴安地块过渡带，该区广泛分布着前寒武纪变质岩系组成的兴华渡口群古老块体。本次研究发现凤凰山地区内还有古老的侵入体——英云闪长岩，零星分布于前寒武纪结晶基底内。本文以凤凰山地区英云闪长岩为研究对象，进行了岩石的主、微量元素测试和LA-ICP-MS锆石U-Pb同位素定年。岩石地球化学特征显示，英云闪长岩属于过铝质钙碱性岩石系列岩石，富集Rb、K等大离子亲石元素（LILE），亏损Nb、P、Sr、Ta、Ti等高场强元素（HFSE），呈中等负铕异常（δEu=0.64~0.69），表现出火山弧花岗岩的特征。英云闪长岩的锆石呈长柱状，具有清晰的环带，显示出岩浆锆石的特征，其LA-ICP-MS锆石U-Pb年龄为（807.7±2.2）Ma，表明其侵位时代为新元古代。结合区域构造演化史，认为该地区新元古代英云闪长岩的形成受Rodinia超大陆裂解-碰撞影响，是额尔古纳地块和兴安地块过渡带地壳增生的产物。

Fenghuangshan is located in the transition zone between Erguna block in the north part of Daxing＇anling Erguna and Xing＇an block, where the Neoproterozoic granites are widely developed. According to this study, we found an ancient intrusive tonalite scattered within the Precambrian crystalline basement in Fenghuangshan area. Taking the tonalite developed in the Fenghuangshan area as the study object, we conducted an analysis for its geochemistry and zircon LA-ICP-MS U-Pb dating. The geochemical characteristics show that the tonalite belongs to per-aluminous calc-alkaline rock series, and the trace element compositions are characterized by enrichment of large ionic lithophile elements （LILEs; e.g., Rb, K）,depletion of high field strength elements （HFSEs, e.g., Nb, P,Sr,Ta and Ti）, and medium negative Eu anomaly （δEu=0.64-0.69）,the geochemical characteristic of volcanic arc granite. The zircons from tonalite occurred as columnar in shape with fine-scale oscillatory growth zoning, showing a magmatic origin for these zircons, yield a weighted mean age of （807.7±2.2）Ma, which indicate that tonalite formed in Neoprpterozoic. Combined with the evolvement history of regional tectonics, we inferred that the formation of the tonalite in Fenghuangshan area was affected by the breakup and collision of Rodinia supercontinent, which is the product of crustal accretion of Erguna and Xing＇an block.