Abstract: The Mesozoic volcanic rocks are extensively developed in the Heihe area of Heilongjiang Province, but their geological dating, rock assemblage, petrogenesis and tectonic setting remain unclear. This paper focuses on the petrology and geochemistry of volcanic rocks in this area. Our study showed that the volcanic rocks formed in the Early Cretaceous. They comprise mainly of andesite, dacite and rhyolite, but also contain trachyte, latite, basaltic andesite, trachydacite, shoshonite and benmoreite. The rock assemblage therefore is of arcvolcanic rock assemblage. These rocks mostly belong to the subalkaline series with Na2O/K2O ratio>1.2 in general. The rock assemblage is metaluminousperaluminous in the A/CNKA/NK diagram. Other rock series of lesser quantity were also shown in the oxide phase diagrams: both calcalkaline (including low Fe calcalkaline (LFCA) ) and tholeiitic (TH) series in SiO2TFeO/MgO diagram, highK calcalkaline and mediumK calcalcaline series in SiO2K2O diagram, calcalkaline/alkacalcline and alkaline (CA+AC+A) series in  SiO2(Na2O+K2O-CaO) diagram, and experimental basaltic and magnesium andesitic melting ranges in SiO2MgO diagram. The rocks were enriched in LILE (K, La, Zr, Hf, Tb and Tm) and depleted in HFSE (Nb, Ta, Ti, Y and Yb). They were relatively enriched in LREEs and slightly depleted in HREEs with  weak negative Eu anomaly. Most of the rocks had high Sr and low Y contents, some displayed adakite characteristics. Overall, the geochemical characteristics were consistent with arc volcanic rocks and in accordance with the rock assemblage. Taking into account tectonic setting discrimination result, we propose that the volcanic rocks were formed in subducted oceanic zones, and the magma source areas were likely subducted oceanic crust, upper mantle wedge, and lower crust of Xingan Arc.

Key words: Heihe area in Heilongjiang Province, Early Cretaceous, volcanic rocks assemblage, arcvolcanic rocks, subduction setting