Abstract: There are large quantities of volcanic rocks in the south of the eastern section of Beishan area's Hongshishan-Baiheshan-Pengboshan ophiolitic belt. The age of rhyolite indicated by LA-ICP-MS zircon U-Pb is (318.5±1.2) Ma, Late Carboniferous. The rhyolite has 77.05%~77.52% of SiO₂, and 6.96%~7.83% of K₂O+Na₂O. Large ion lithophile (Rb,K,Th,U,Zr,Hf) enrichment and high field strength elements (Ta,Nb,Ti) shortage are displayed in the primitive mantle normalized trace element spider diagram. The petrogeochemical features indicate that the rhyolite shows high potassium calc alkaline series, with the volcanic arc granite attribute. Combined with the study of regional geological characteristics, it indicates that Hongshishan-Baiheshan-Pengboshan extensional faulting formed the initial small ocean basin. Namely, it's similar to the Red Sea Type trough environment in Early Carboniferous. The oceanic crust subducted into the south and the north directions in late Early Carboniferous. And the southern edge of the consistently cleaving small ocean basin subducted into the south direction by the Late Carboniferous, so large amounts of arc volcanic rocks formed.