Abstract: This paper discusses the rock genesis and tectonic environment of the monzonitic granite from the Muztag area in the western part of the East Kunlun orogenic belt, and provides new information for the tectonic evolution of the East Kunlun orogenic belt, through the study of zircon U-Pb ages and geochemical data.LA-ICP-MS zircon U-Pb dating of the medium-coarse and medium-fine grained monzogranites from the Muztag area yield ²⁰⁶Pb/²³⁸U ages of 415±4 Ma(MSWD=2.9) and 419±6 Ma(MSWD=4.3), respectively.These geochronological data show that the intrusive rocks were formed in the Early Devonian.Whole-rock geochemical results suggest that the monzonitic granite samples of the Muztag area are characterized by high silicon, low titanium and magnesium contents, as well as large Aluminum Saturation Index(A/CNK) values.These are indicative of calc-alkaline weakly peraluminous granitic series.Moreover, the monzonitic granite samples are relatively enriched in light rare earth elements(LREE) and Rb element, but depleted in high field-strength elements of Nb, Ta, Yb and Y.In combination with the moderate values of CaO/Na₂O, low values of Al₂O₃/TiO₂and regional geological data, it is proposed that monzonitic granite of the Muztag area could be formed in the syn-collision tectonic environment and be derived from the continental crust with characteristics of deficient-clay sediments.By compiling previous studies of the East Kunlun belt, it is suggested that closure time of the Proto-Tethys ocean in the East Kunlun orogenic belt has significant spatio-temporal difference characterized by trending from north and central to south direction vertically and by shifting from east to west in the horizontal direction.