Abstract: The Dongquangebi pluton is located in the Wushitala area of the northern margin of the South Tianshan, and is comprised mainly of porphyraceous monzonitic granite and a small amount of mafic microgranular enclaves. SHRIMP zircon U-Pb dating of porphyraceous monzonitic granite indicates that the weighted mean 206Pb/238U age is 305±1 Ma. These rocks are characterized by high-alkali (K2O+Na2O=7.58%~8.44%) and high-K (K2O/Na2O=1.09~1.33) and high Mg number (Mg#=51.6~58.5), with the A/CNK values between 0.92 and 1.00, which fall into the metaluminous high-Mg# and high-K calc- alkaline series. These rocks are also characterized by enrichment of LREE and LILE (Rb, K, Th and U) and depletion of HREE and HFSE (Nb, P and Ti), with slightly negative Eu anomaly (0.60~0.99) and strong depletion of Y (10.17×10-6~14.84×10-6) and Yb (1.054×10-6~1.374×10-6). These features suggest that the petrogenesis of the Dongquangebi pluton is magma mixing and the geochemical features of the Dongquangebi pluton belong to granitic rocks formed in the late-stage of a collisional orogeny. Combined with regional geological data, it is concluded that the Dongquangebi granitic pluton was derived from partial melting of the lower crust,with minor mixing with mantle-derived magma,due to the underplating of mantle-derived magma during the late-stage collision between the Tarim plate and Yili-Central Tianshan plate. The collisional magmatism in the South Tianshan indicates that the South Tianshan Late Paleozoic residual basin was closed in the Late Carboniferous, and the establishment ofmagma mixing of the Dongquangebi pluton indicates an important event of vertical growth of the continental crust in the South Tianshan.

Key words: high-K calc-alkaline granite;zircon SHRIMP U-Pb age;magma mixture;late-stage of collisional orogeny;South Tianshan