Detailed field work helped identify threedifferent assemblages of rocks occurring in the Hebukesaier ophiolitic mélange in the northern region of West Junggar. They are typical ophiolite unit mainly consists of metamorphic peridotite, gabbro, diabasic dike, basalt and chert; ocean island unit mainly consists of OIB, which coexists closely with silicolit, silica mudstone and limestone; and postcollision volcanic rock unit is mainly metarhyolite. Gabbro and diabase in ophiolite are characterized by slight enrichment or depletion in light rare earth elements and low (a/Yb)N ratios of 054~318, no obvious Eu anomalies, indicating that both are of EMORB and NMRB characteristic. The ocean island basalt shows relatively high contents of Al2O3 (366%~1583%), TiO2 (262%~315%) and Na2O+K2O (571%~7%), and displays an obvious rightleaning pattern with a high content of rare earth elements. Metarhyolites exhibit relatively high SiO2 and K2O contents, and extremely low MgO, CaO and MnO contents, enrichment of incompatible elements (K, Rb, Th, U and Pb), obvious depletion of Sr, P and Ti, and weak depletions of Nb and Ta. Geochemical characteristics indicate that metarhyolites may be formed in a postorogenic extension setting. LAICPMS UPb 〖JP2〗dating on zircons from metarhyolite yieldes a weighted mean 206Pb/238U〖JP〗 age of 435±2 Ma. Metarhyolites cut through or intruded different units of ophiolite (peridotite, diabase and basalt), suggesting that the Paleoocean basin of Hebukesaier ophiolite had been closed before late Early Silurian.