Zircon U-Pb chronology, geochemistry of the Taergen granite in Western Junggar, Xinjiang, and their geological significance

There are large numbers of intermediate-acid intrusions distributed along the Darbut tectono-magmatic belt in Western Junggar, Xinjiang. It is of great significance to understand the regional magmatic evolution through their petrogenesis and emplacement periods. The formation time, petronenesis and tectonic setting of Taergen granites, located in the northern part of Mayile Mountain, are reported in this study through field observation, LA-ICP-MS zircon U-Pb dating and geochemical analysis. The Taergen granites are mainly composed of monzonitic granite and syenogranite, LA-ICP-MS zircon U-Pb dating of monzonitic granite yielded an age of 296.6±2.0Ma (n=27, MSWD=0.33), corresponding to early Early Permian. Petrogeochemical analysis indicates that Taergen granites are characterized by high silica, alkali, low titanium and aluminum, lean calcium and magnesium. They are also enriched in large ion lithophile elements (e. g. Rb, Th, K) and high strength field elements (e. g. Zr, Hf) and are strongly depleted in Sr, Eu, P, Ti and mediate depleted in Ba, Nb, Ta, with high 10⁴Ga/Al ratios and Zr+Nb+Ce+Y contents. These features indicate that Taergen granites are metaluminous to weakly peraluminous alkaline series A-type granite, which were originated from the partial melting of felsic crust under high temperature and low pressure conditions. Combined with regional tectonic evolution and previous results, we suggest that the Western Junggar region was still in a subduction-dominated setting in the Late Carboniferous-Early Permian, and probably associated with the ridge subduction during Late Carboniferous period.