Abstract: Ar Horqin Banner area is located in the eastern XinganMongolian orogenic belt, and the Mesozoic magmatic rocks are widely distributed. In this paper, zircon UPb geochronological and element geochemical studies were carried out for the Late Jurassic intrusive rocks in Ar Horqin Banner area. The study of petrology indicates that the granitoids are mainly composed of quartz monzobiorite, quartz diorite and biotite granodiorite. Zircon LAICPMS UPb dating of the biotite granodiorite gives a weighted average age of (14379±084) Ma(MSWD=33), indicating that it belongs to the Late Jurassic, and it is during regional MoAuCu metallogenic peak period. Major elemental geochemistry shows that the rocks are quasialuminous calalkaline granites, which is characterized by relatively rich alkali. Trace elements have a similar variation trend of low REE contents and obvious fractionation of light and heavy rare earth, significant negative anomaly of Eu, the enrichment of strong incompatible elements (Rb, Th, U, LREE), depletion of high fieldstrength element (P, Ti, Y and HREE), relative depletion in Nb, Ta and Ba. Main body of the granites belongs to calcalkaline I genetic type. The magmas were the product of partial melting of the basite in the crust, formed in an extensional setting after the collision, which is a favorable metallogenic tectonic evolution stage. SI, K/Rb and Rb/Sr ratios are relatively small, DI values and Fe2O3/FeO ratios are relatively large, which shows that the granites belong to mediumstrong evolution, medium fractionated, oxidation type or magnetiteseries. Their geochemical ore parameters indicate that Cu, Au, Mo mineralization potentiality decreases systematically, consistent with the other mineralization characteristics in the study area.

Key words: Ar Horqin Banner, Late Jurassic, Itype granite, extensional setting, mineralization potentiality