Geological characteristics and age determination of the Palaeoproterozoic Gudongjing Group complex in the Beishan Mountain, Gansu Province

There are abundant outcrops of Gudongjing Group in Beishan region without paleontological fossil, therefore its strati-graphic age was previously determined by regional stratigraphic correlation and the Sm-Nd isochron age obtained from the overlying strata and underlying layer, resulting in no precise age for Gudongjing Group. In this study, the authors applied LA-ICP-MS and SHRIMP methods to determine isotopic age of detrital zircon in Gudongjing Group with the purpose of obtaining its age. The youngest age of detrital zircon is 1213±24Ma and it is considered to be the lower age limit. The detrital zircon age of 3110±6Ma and 2786±7Ma may indicate ancient remnants of the Earth's crust in Beishan micro-block, and Gudongjing Group may be one of the metamorphosed basements in Beishan. Three continuous peak ages (1750Ma, 1580Ma and 1470Ma) show that the provenance of most quartzite in Gudongjing Group went through the Luliang movement. Therefore, the results of this study can serve as powerful evidence for completing the stratigraphic framework in Beishan.