北祁连东段新元古代火山岩的发现及其特征和形成环境

FEATURES OF THE LATE PROTEROZOIC METAMORPHIC VOLCANIC ROCKS IN THE EASTERN PART OF THE NORTHERN QILIAN MOUNTAINS AND THEIR TECTONIC SETTING

1/ 5万石门川幅、老龙湾幅区域地质调研结果表明 ,北祁连东段上吊吊坡地区存在新元古代火山岩 ,Sm- Nd同位素测试结果为 72 3.1± 2 5.0 Ma。地球化学特征揭示该套火山岩为拉斑玄武岩系列 ,稀土、微量元素特征及 Nd同位素特征证明其形成于岛弧环境 ,它是中国大陆在元古代晚期固结过程的产物 。

According to the geological survey on the scale of 1∶50,000 in the Shimenchuan and Laolongwan areas, the late Proterozoic volcanic rocks formed about 723 million years ago, and measured by isotope Sm-Nd, have been found in the eastern part of the northern Qilian Mountains. The geochemical features indicate that the volcanic rocks belong to tholeiite system, and that they developed in an island-arc environment based on the analyses of rare earth elements and microelements, along with the isotope Nd. These volcanic rocks resulted from the process of consolidation of the China continent taking place during the Late Proterozoic, which fit with the tectonic setting in the north China terrain.