Late Triassic calc-alkaline I-type granites with abundant mafic microgranular enclaves (MMEs) are widespread in the West Kunlun Orogenic Belt, meanwhile, large quantities of Mesozoic granitic pegmatites also develop in this area, which makes an important pegmatite-type Li-Be metallogenic belt in China. In recent years, a great breakthrough in mineral resource prospecting has been made in Dahongliutan area, especially in the Qitaidaban pluton which is closely related in space with the pegmatite-type lithium deposits in this area. In this paper, we present a systematic research result from petrological, petrogeochemical, zircon U-Pb chronological and Sr-Nd-Hf isotopic studies on the biotite monzogranite and the MMEs in Qitaidaban, West Kunlun, to accurately determine their formation age, petrogenesis characteristics and tectonic settings, and thus to disclose their genetic relationship with rare metal pegmatite mineralization. The LA-ICP-MS U-Pb ages of zircons indicate that the mafic microgranular enclaves and the host biotite monzogranite are crystallized at 212.9 +/- 1.6Ma and 213.7 +/- 2.0Ma, respectively, i.e., in the Late Triassic, which provides strong evidence for the existence of magma mixing in this area. Whole-rock geochemical data indicate that the biotite monzogranite and the MMEs belong to weak peraluminous high-K calc-alkaline I-type granites, and the content of SiO2 in MMEs is lower than that of the host monzogranite. Furthermore, they are enriched in LILE (Rb, Th, U, K), relatively depleting in HFSE (such as Nb, P, Ti), and have similar Sr-Nd-Hf isotopic compositions. The biotite monzogranite has (Sr-87/Sr-86)i values of 0.70789 similar to 0.70839, epsilon(Nd)(t) values of -5.42 similar to-4.02, epsilon(Hf)(t) values of -4.8 similar to 4.8, and Hf isotope two-stage model age (t(DM2)) of 909 similar to 1516Ma; while the enclaves have (87Sr/86Sr)i values of 0.70833 similar to 0.71011, epsilon(Nd)(t) values of -6.36 similar to-5.05, epsilon(Hf)(t) values of -4.7 similar to 1.8, and Hf isotope two-stage model age (t(DM2)) of 1097 similar to 1509Ma, respectively. It is considered that they are the products of the mixing of a basic magma formed by partial melting of enriched lithospheric mantle and a felsic magma formed by melting of amphibolite in ancient lower crust. Based on a combined study of geochronology and evolutionary characteristics of regional structures in the West Kunlun, we consider that the biotite monzogranite and the MMEs in Qitaidaban were formed in the post-collisional extension stage of the Paleo-Tethys Ocean, which suggests that the West Kunlun Orogenic Belt had begun its post-collisional extension in the Late Triassic (213Ma), and thus it provides new chronological evidence for the tectonic and magmatic evolution of the Paleo-Tethys in West Kunlun. The rare metal pegmatites in Dahongliutan area are the products of crystallization and differentiation of the granitic magma which has the characteristics of a continuous differentiation and evolution, while the Qitaidaban granite pluton was formed in the middle of the whole magmatic evolution process, and as a result, it has indicative significance to the formation of rare metal pegmatites in Dahongliutan area.
