Abstract:This study carried out zircon U- Pb dating, lithogeochemistry and Sr- Nd isotope analysis for the Lower Cretaceous felsic volcanic rocks in the northern Zhalantun region of Great Xing’an Range, NE China, with the aim to restrain the petrogenesis and regional dynamic background. Zircon LA- ICP- MS U- Pb dating yielded an weighted age of 141±3Ma (Early Cretaceous) for rhyolite rock of the Manketouebo Formation (D14208) and an weighted age of 135±5Ma (Early Cretaceous) for the trachy dacite rocksof the Manitu Formation (D14210). Geochemcially, two groups of the rocks belong to calc- alkaline series, with SiO 2 values of 76. 41%~78. 01% and 64. 71%~65. 63%, MgO values of 0. 04%~0. 22% and 1. 12%~1. 35%, Mg# numbers of 12~42 and 32~38, enrichment in LILE and LREE, depletion in HFSE and HREE, and Eu/Eu* values of 0. 40~0. 52 and 0. 82~0. 95, respectively. In addition, the rocks have Rb/Sr ratios of 2. 42~3. 21 and 0. 12~0. 15, the K/Rb ratios of 284~290 and 284~306,the Nb/Th ratios of 2. 35~3. 82 and 2. 60~3. 63. ε Nd ( t ) values of 1. 57~2. 22 and 1. 72~2. 24, and t DM2 values of 751~804 Ma and 743~786Ma indicate that the primary magma derived from partial melting of the crust. Together with previous studies of contemporaneous magmatism and tectonism in NE China, the present results suggest that the generation of the rocks was related to the closure of the Mongol- Okhotsk Ocean.
