LA-ICP-MS zircon U-Pb dating yields a weighed mean age of 247±3 Ma for quartzdiorite at Guokeshan area. These rocks consist of plagioclase (55% to 60%）, quartz (15% to 20%）, hornblende (10% to 15%) and biotite (5% to 10%) and belong to metaluminous to weakly peraluminous with A/CNK values varing from 0.95 to 1.02, indicating Itype granite affinity. They are characterized by enrichment of LREEs and LILEs (eg., K, Rb, Cs, Ba, Th) and depletion of HREEs and HFSEs (eg., Nb, Ta, P, Ti）, which are consistent with typical features of arcmagmatite. In addition to the presence of abundance mafic microgranular enclaves in samps, they exhibit higher MgO contents (ranging from 2.04% to 2.44%) and Mg# values (ranging from 48.9 to 51.9) than experimental melts generated by partial melting of metabasalts/pelites at 1 to 4 GPa, suggesting that they were derived from by magmas mixing between magma produced by partial melting of amphiboite in lower crust and magma derived from enrich mantle. The low Tiinzircon temperatures and high zircon Ce4+/Ce3+ ratios indicate zircons were crystallized from low temperature and high oxygen fugacity magmas, and the involvement of waterbearing melts/fluids during the formation of the magmas. All samples fall into the fields of volcanic arc granite in the granite tectonic environment discrimination diagrams, and show high La/Nb ratios (ranging from 2.27 to 2.64)， which are consistent with active continental margin area (>2.0）. Combined with regionally geological setting, we suggest that the Guokeshan quartzdiorites are formed as a continental margin arc by the northern subduction of PalaeoTethys ocean.