NEW RECOGNITION OF THE AGE OF THE LEBAQUAN GROUP IN BEISHAN MOUNTAIN,GANSU

The Lebaquan Group in the Beishan Mountain area, Gansu Province, is a medium- to high-grade schist and mica-quartz schist, locally intercalated with marble, gneiss and magnetite. Its age assignment has long been disputed. Through field work, the authos have ascertained that this group has faulted contact with the Silurian Gongpoquan Group. The sample taken from amphibolite dikes intruded into this group were measured to have a Sm-Nd isochron age of 644.5±49Ma. According to regional correlation rock associations and degrees of deformation and metamorphism of this group and the occurrence of metamorphosed sedimentary iron deposits, the authors consider that the Lebaquan Group is stratigraphically equivalent to the Baihu Group adjacent it and that its age should be the Changchengian Period.