LA-ICP-MS zircon U-Pb dating of the Kubusunan granodiorite in the Kalamaili area, eastern Junggar, Xinjiang

Abstract：LA-ICP-MS zircon U-Pb dating of the Kubusunan granodiorite and its enclaves in the Kalamaili area, eastern Junggar, Xinjiang, indicates an age of 287±2 Ma (MSWD=0.15) for the granodiorite and an age of 286±3 Ma (MSWD=0.22) for its enclaves. The two ages are the same within the error limits, suggesting that granodiorite and dark enclaves formed synchronously. Enclaves resulted from magma mixing, i.e. they were the result of mixing of supercool mafic magma into intermediate-acid magma and then fast condensation. In the process of magma mixing，basic magma of enclaves and acid magma of host rocks changed their components by chemical diffusion, and thus enclaves were modified and assimilated by granodiorite magma. This might be why the Kubusunan granodiorite and its enclaves have the same LA-ICP-MS U-Pb zircon age. The ages of the Kubusunan granodiorite is in the range of 330-265 Ma for post-collisional magmatic activity in East Junggar, slightly younger than the age (300± Ma) of the Wulungu River alkali granite and Kalamaili alkali granite, all being the product of post-collisional magmatic activity at peripheries of East Junggar, and their formation and evolution indicate that underplating of post-collision mantle-derived magma in Junggar resulted in vertical growth of continental crust.