Abstract: The connecting relationship of the West Qinling and the East Qinling is a hot spot in geologic research in recent years.The Caotangou volcanic rock outcrop in the area connecting the West Qinling and the East Qinling is the key to resolve this scientific question.Geochemical research demonstrates that the Caotangou volcanic rockis characterized by low TiO₂、REE contents,and high Al₂O₃ content.The chondrite-normalized REE distribution pattern showflat to slightly enrichment characteristics,the trace element sare characterized by enrichment in Cs,Rb,Ba and Th contents,intensive depletion in Nb and Ta contents,and the unfractionated HFSE elements.The characteristics of Nb,Ta,Zr,Hf contents and Nb/La,Hf/Ta,La/Ta,Ti/Yvalues indicate these volcanic rocks are inf luenced by the input components derived from the subduction-zone fluid in their magma source,similar to typical island arcbasalt.From the study of geology and geochemistry,it can be suggested that the Caotangou volcanic rock could be compared with the meta-volcanic rock of Danfeng group which were magmatic product from the subduction-zone during the closing of Qinling ocean in early Palaeo zoic.The Caotangou volcanic rocks present the west part of the Shangdan Suture.Strent ching to the west,it could connect with the Guanzizhen-Wushan ophiolitic mélange in the West Qinling area.