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

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.