内蒙古北部早元古代变质岩系的发现及其岩石学研究

DISCOVERY OF EARLY PROTEROZOIC METAMORPHIC COMPLEX IN NORTH INNER MONGOLIA

笔者参加内蒙区调工作，首次于本区发现了早元古代变质岩系。该岩系由３个岩组组成，一是花敖包特正变质岩组（Ｐｔ１ｂｈ），二是昌特敖包副变质岩组（Ｐｔ１ｂｃ），三是阿木乌苏条带状混合岩组（Ｐｔ１ｂａ）。对各岩组的岩石学、矿物学及岩石化学的研究，表明这是一套深变质岩系，近似于下地壳岩石组合。其Ｒｂ－Ｓｒ等时线测年资料与印支期花岗岩源区年龄为１７～１９亿ａ，是目前本区发现的最古老的变质岩系，它经历了大面积混合岩化和花岗岩化作用。

he Early Proterozoic metamorphic complex in the north Inner Mongolia,firstly found in regional geological surveying, consists of three sets of the Huaaobot orthometamorphite (Pt1bh), the Changteaobo parametamorphite (Pt1bc) and the Amuwusu migmatite (Pt1ba).The studying of the petrology, mineralogy and petrochemistry of these segments shows that metamorphic complex is a set of plutonic metamorphic rock and similar to the rock association of the lower crust. The age by Rb-Sr isochron dating of the Changteaobo parametamorphite (Pt1bc) and the age of source rock of Indo-Chinese migmatic granite is 1 700～1 900 Ma which is considered to be the oldest rock association in this region. The metamorphic complex had been migmatized and granitized widely in Hercynian-Indo-Chinese period .