内蒙古吉日嘎朗图晚泥盆世侵入岩特征及其构造意义

内蒙古锡林浩特吉日嘎朗图晚泥盆世侵入岩分布于内蒙古自治区二连-贺根山板块对接带北部,其岩石组合为石英闪长岩、英云闪长岩和花岗闪长岩.岩石化学成分SiO2含量为64.23%～74.47%,Al2O3为13.59%～16.26%,TiO2为0.19%～0.76%,Na2O+K2O为6.28%～8.15%,属钙碱性系列,A/CNK=1.06-1.21,属过铝质花岗岩.An-Ab-Or图显示T2G1G2QM组合,属TTG岩类.微量元素显示为火山弧花岗岩.稀土元素以高度分馏的稀土模式和亏损HREE为特征,显示TTG岩类特征.综合反映该套岩石具典型TTG岩类特征,显示为洋壳向陆壳俯冲的产物.在花岗闪长岩中取单颗粒锆石U-Pb年龄为361.1±1.0Ma,为晚泥盆世侵入岩,因此,西伯利亚板块与华北板块的缝合时间至少应当在晚泥盆世之后.

CHARACTERISTICS AND TECTONIC SIGNIFICANCE OF THE LATE DEVONIAN INTRUSIVE ROCKS IN JIRIGALANGTU, INNER MONGOLIA

The Late Devonian intrusive rocks in Jirigalangtu,Inner Mongolia are distributed on the northern side of the Erlian-Hegenshan connect zone,with rock association of quartz diorite,tonalite and granodiorite.Lithochemically,the rocks are assigned to calk-alkaline series,with contents of SiO2for 64.23%-74.47%,Al2O3 for 13.59%-16.26%,TiO2 for 0.19%-0.76% and Na2O ＋ K2O for 6.28%-8.15%,with A/CNK ratio of 1.06-1.21,belonging to peraluminous granites.The An-Ab-Or diagram shows the T2G1G2QM assemblage,which belongs to TTG type.The trace elements display the characteristics of volcanic arc granite.The rare earth elements are characterized by high fractionation and deficient HREE.The characteristics of the intrusive rocks reflect typical TTG resulted from the subduction of oceanic plate towards continental plate.The single zircon U-Pb isotopic age of the granodiorite is 361.1 ± 1.0 Ma（Late Devonian）.Therefore,the matching time of Sino-Korean plate and North China plate should not be earlier than Late Devonian.