Abstract:

Three representative plutons, Wutubulak, Areletuobie and Hadansun, in the lower reaches of the Qinggeli river in the northern part of East Junggar, Xinjiang were chosen for Rb-Sr isochron dating.The results show that the formation-ages of granitic plutons in the southern side of the Mayin'ebo fault in the researched area are （334.1±9.5） Ma, （300±9） Ma and （280±12） Ma with the initial ⁸⁷Sr/⁸⁶Sr ratios of 0.70433, 0.70435 and 0.70384, respectively, and that they were generated at different stages of middle-late Variscan Movement. The Wutubulak pluton, which formed at Early Carboniferous, belong to calc-alkaline series, was likely produced by partial melting of the Early Devonian Nb-enriched basalts during post-collisional event. In combination with the previously assumed plate subduction time (408-376 Ma), the collision of Siberian Plate  with Kazakstan-Junggar Plate can be limited within the range of 376-334 Ma. The Areletuobie pluton formed in an extensional setting subsequent to post-collision, and it is inferred to be generated by partial melting of intermediate-basic volcanic rocks that might form in an island arc setting. Although the Hadansun pluton also formed in an extensional environment of post-collision, it might be related to magma underplating under a strong extensional environment

Key words: Rb-Sr isochrone age, granitoid, collision, underplating, northern part of East Junggar, Xinjiang