College of Earth Sciences, Jilin University, Changchun 130061, China

Petrography, geochronology and geochemistry of the Middle-Late Mesozoic volcanic rocks in Deerbuer area in Genhe City, Inner Mongolia, located in the northern part of the Great Xing'an Range, have been studied to explore the tectonic evolution in this area.The existence of the Early-Middle Jurassic volcanic rocks can be inferred,according to the stratigraphic contacts and dating of previous studies in the region.LA-ICP-MS zircon U-Pb dating shows that the age of Manketouebo Formation is (155±1.8) Ma of the Late Jurassic. The dates of Manitu Formation are (124.1±0.8)Ma and (122.8±1.3)Ma, indicating the petrogenic age as the Early Cretaceous.The Early-Middle Jurassic volcanic rocks belong to high-K calc-alkaline series, quasi-aluminous volcanic rocks, with intense enrichment in LILEs (Ba,Sr) and depletion in HFSEs (Nb,Ta), implying that the rocks were formed in the tectonic setting of active continental margin. The Manketouebo Formation is composed of peraluminous high-silica rhyolite, which is enriched in silicon and K, depleted in Na and Ca, and the ratio of Rb/Sr is 4.1 to 10.3, with the characteristics of S-type granite. It is the product of further evolution of magma under MUSH model in magma chamber, which originally formed by the partial melting of thickened lower crust. LREE and HREE of the volcanic rocks of Manitu Formation show obvious fractionation. The volcanic rocks have the characteristics of A-type granite, with enrichment of Zr, Rb, Th and U, and depletion of Sr, Ba, Nb, Ta, P and Ti, and formed by crustal decompression melting in extensional background. Combined with previous research, it is concluded that the Middle-Late Mesozoic volcanic rocks in the Great Xing'an Range were mainly controlled by the Mongolia-Okhotsk Ocean tectonic domain. In the Early-Middle Jurassic, the Mongolia-Okhotsk Ocean crust experienced southward subduction, and in the late Middle Jurassic, the Mongolia-Okhotsk Ocean was closed, and the Siberian Craton collided with Sino-Korean and Mongolian plates. In the Early Cretaceous, the Great Xing'an Range was in an extensional tectonic environment.