This paper is the result of geological survey engineering. Objective Dunhuang block is located at the junction of Tarim Plate, Central Asian Orogenic Belt and Qilianshan Orogenic Belt. Its formation age and tectonic attributes have always been controversial. This paper takes the intermediate–acid volcanic rocks exposed in the northeastern margin of Dunhuang block as the research object, and attempts to provide evidence for solving the above problems. Methods In this paper, LA–ICP–MS zircon U–Pb dating of three dacite samples and geochemical analysis of intermediate–acid volcanic rocks were carried out to explore the formation age, petrogenesis and tectonic attributes of the volcanic rocks. Results LA–ICP–MS zircon U–Pb geochronology indicates that three dacite samples form at (533.2±6.1) Ma, (527.7±6.1) Ma and (514.9±3.4) Ma, belonging to Early Cambrian. The andesite exposed in the area has typical characteristics of high–Mg andesite, e.g., SiO₂ contents (51.4%–55.98%), high MgO contents (5.81%–12.31%) and Mg^# values (59–72), high Cr (166×10^–6–1020×10^–6) and Ni (41.4×10^–6–169×10^–6) contents, and low FeO^T/MgO (0.79–1.56) ratios. Otherwise, the andesites have high Ti/Zr, Ti/Y ratios and low Rb/Sr ratios, high La/Nb and Ba/Nb and Ba/La ratios. The intermediate–acid volcanic rocks are enriched in large ionic lithophile elements (Rb, Ba, U, K) and light rare earth elements, depleted in high field strength elements (Nb, Ta, Zr, Ti) and heavy rare earth elements, with characteristics of near–flat right–leaning rare earth distribution pattern, low Nb/La (0.36–0.46) and Hf/Th (1.02–1.34) ratios, high Hf/Ta (5.71–8.60) and La/Ta (21.72–29.50) ratios, indicative of the geochemical properties of island arc volcanic rocks. Conclusions It is considered that the volcanic rocks should be the Early Cambrian volcanic caprock above Dunhuang Group. The volcanic rocks in the area should be formed in the island arc environment, which may be formed by partial melting of metasomatic mantle wedge in the subduction of the Early Cambrian Paleo–Asian Ocean crust melt (fluid), and contaminated by crustal materials during the ascending process. According to the formation age of volcanic rocks and the characteristics of petrogeochemistry, the subduction of the Paleo–Asian Ocean can be traced back to the Early Cambrian.