THE AGE OF THE DASHIQIAO FORMATION IN LIAOHE GROUP: Constraints from LA-ICP-MS Zircon U-Pb Dating of Acidic Volcanic Rocks

Dashiqiao Formation, the important ore-bearing horizon in Liaohe Group, is lithologically composed of dolomite marble, calcite marble and mica schist. In this study, a layer of acidic volcanic interbed, rhyolitic breccia tuff, is founded in the marble of Dashiqiao Formation for the first time in Bahui Town, southern Liaoyang City. Based on the field occurrence, the acidic volcanic rock and the marble were deposited simultaneously. The clear oscillatory zoning and high Th/U ratio show that the zircons from the rhyolitic breccia tuff are magmatic origin. The LA-ICP-MS zircon U-Pb dating yields the age of 2171±11 Ma, which is the first accurate age for the Dashiqiao Formation. This age also constrains the sedimentary time of Langzishan Formation, Lieryu Formation and Gaojiayu Formation, which underlie the Dashiqiao Formation, to before 2171 Ma.