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内蒙古科尔沁右翼中旗敖兰三队侵入体的同位素年代学及岩石地球化学研究表明,敖兰三队侵入体巨晶正长花岗岩具有低Sr、高Yb型花岗岩特征,其LA-ICP-MS锆石~(206)Pb/~(238)U年龄加权平均值为220±1Ma,表明该侵入体是晚三叠世早期侵位形成的。岩石高硅、富碱、高铁镁比、贫钙、贫镁和低钛;稀土元素配分曲线呈现“海鸥式”分布特征,显示强烈的Eu负异常。微量元素特征显示较低的Sr、Ba含量,较高的Yb、Zr和Y含量,在微量元素原始地幔标准化蛛网图上显示明显的Sr、Ba和Ti的负异常。岩石具有高的Rb/Sr和Rb/Nb,显示出壳源岩浆的成分特征。综合分析表明,本区巨晶正长花岗岩为低压下地壳部分熔融的产物。根据(Y+Nb)-Rb、(Yb+Ta)-Rb、Nb-Y-Ce三角图解,并结合区域构造演化,认为巨晶正长花岗岩形成于造山后伸展的构造环境。在中—晚三叠世,内蒙古科尔沁右翼中旗地区构造体制经历了重要的转变,由挤压体制转变为造山后软流圈上涌、岩石圈减薄。
The isotopic geochronology and geochemistry of the intrusive bodies of the Ao Lan Third Team from the Horqin Right Wing Middle Banner in Inner Mongolia show that the intrusive giant granitoids of the Ao Lan III Formation have the characteristics of low Sr and high Yb granites and their LA-ICP-MS zirconium The weighted average Pb ~ (238) U ages of ~ (206) Pb are ~ 220 ± 1Ma, indicating that the intrusion was formed during the early Triassic emplacement. Rock high silicon, alkali-rich, high-iron-magnesium ratio, poor calcium, poor magnesium and low titanium; Rare earth elements distribution curve showed “gull ” distribution characteristics, showing a strong Eu negative anomaly. The characteristics of trace elements show lower contents of Sr and Ba and higher contents of Yb, Zr and Y, which show obvious negative anomalies of Sr, Ba and Ti on trace elements normalized mantle. Rocks have high Rb / Sr and Rb / Nb, showing the compositional features of the crustal magma. Comprehensive analysis shows that the giant granite is the product of partial melting of the crust under low pressure. Based on the (Y + Nb) -Rb, (Yb + Ta) -Rb and Nb-Y-Ce triangle diagrams and the regional tectonic evolution, it is considered that the giant granitoids are formed after the orogenic extension. During the Mid-Late Triassic, the structural system of the Horqin-Zhongzhong Middle Banner in Inner Mongolia has undergone an important transition from the squeeze system to the upwelling of the asthenosphere and the thinning of the lithosphere.