Geochronology, Geochemistry and Tectonic Significance of Late Triassic Adakite Granites in Tanchang-Zhouqu area of West Qinling

The west Qinling orogenic belt is located in the west of Qinling-Dabie orogenic belt. The study of granites is of great significance for understanding the tectonic evolution of the central orogenic belt. In this paper, Petrography, LA-ICP-MS zircon U-Pb chronology and geochemistry of the Yanmaiceng and Hanban granitoids in the Tanchang-Zhouqu area of the Western Qinling Mountains were studied. The results show that the Yanmaiceng monzodiorite and HanBan granodiorite are characterized by high Al₂O₃, MgO, Mg^# < 45, rich in Na and poor in K. The main –granites are subalkaline–alkaline series, quasi-aluminous～weakly peraluminous I-type granites, which are highly enriched in LREE, weak negative Eu anomaly, and enriched in LILE such as Th, K, U. The elements of Nb, Ta, P and Ti in HFSE were strongly depleted. Zircon U-Pb isotopic dating shows that the Yanmaiceng and Hanban granitoid were formed at (219.4±1.5) Ma and (222.1±1.9) Ma, respectively, and emplaced in the middle of Late Triassic. According to the geological, geochemical and chronological characteristics, the granites in the study area are in a post-collision environment, which may have been formed in the crust thickening, and the lower lithospheric mantle detachment occurred, resulting in the upwelling and thickening of the asthenosphere and the partial melting of the lower crust.