内蒙古北山北缘蓬勃山一带古亚洲洋闭合时间制约——来自黑红山二长花岗岩的证据

黑红山二长花岗岩分布于红石山-百合山-蓬勃山蛇绿岩带北部,地球化学特征显示其属于准铝质-弱过铝质、中-高钾钙碱性系列,为高分异的I型花岗岩;轻稀土元素富集,轻、重稀土元素分馏明显,具弱负Eu异常,稀土元素曲线为右缓倾。微量元素相对富集Ba、K、Zr、Hf,亏损Ta、Nb、P、Ti,显示与俯冲有关的侵入岩特征,形成于碰撞前的火山弧环境。LA-ICP-MS锆石U-Pb定年获得~(206)Pb/~(238)U年龄加权平均值为315.2±2.5Ma。综合研究表明,黑红山地区在晚石炭世属于活动大陆边缘的火山弧,红石山-百合山-蓬勃山蛇绿岩带所代表的洋盆在此尚未消亡。

Time constraint on the closing of the Paleo-Asian Ocean in northern Beishan of Inner Mongolia: Evidence from Heihongshan admellite

The Late Carboniferous admellite in the Heihongshan area is located in the northern part of the Hongshishan-Baiheshan-Pengboshan ophiolite belt. The geochemical characteristics show that the admellite belongs to metaluminous to weakly peralic potassium aluminous calc alkaline series I type granite of high differentiation; its LREE enrichment and LREE and HREE fractionation are obvious, with weak Eu negative anomaly and right-inclined rare earth curve. Trace elements are relatively enriched in Ba, K, Zr and Hf but depleted in Nb, Ti, P and Sr, indicating the characteristics of intrusive rocks related to subduction and formed in the volcanic arc environment before collision. The U-Pb dating of LA-ICP-MS zircon yielded weighted average ²⁰⁶Pb/²³⁸U age of 315.2±2.5Ma. Comprehensive studies show that the Heihongshan area belonged to the volcanic arcs on the active continental margin in the Late Carboniferous epoch, and the Hongshishan-Baiheshan-Pengboshan ophiolite belt suggests that the oceanic basin in Heihongshan area was closed in the Late Carboniferous epoch.