Geochemical characteristics and zircon U-Pb age of the intermediate and acid volcanic rocks from Yuanbaoshan area in the northern part of Beishan orogenic belt

The Late paleozoic intermediate and acid volcanic rocks from Yuanbaoshan area in the northern part of Beishan orogenic belt are dominated by dacitic rock with a small amount of andesitic rock. Zircon U-Pb isotopic age 315.9±3.4Ma was obtained in the dacitic tuff. It means that the age of rock formation is Late Carboniferous. The authors consider that this set of volcanic rocks belong to Upper Carboniferous Ganquan Formation. This set of volcanic rocks have the characteristics of ocean island arc and continental margin arc and are of low potassium-medium potassium calc-alkaline series, enriched relatively in light rare earth elements and large ion lithophile elements, and relatively depleted in high field strength elements, with unconspicuous Eu-negative anomaly. Combined with previous studies of regional structures and geochemistry of volcanic rocks, the authors consider that Ancient Asian Ocean still subducted and had not yet been closed in the north part of Beishan orogenic belt in Late Carboniferous.