Abstract:The Lhasa terrane has undergone subduction, subtraction and land-land collision of the New Tethys Ocean, and a large area of intermediate-acid intrusive rocks have emerged, which provides favorable conditions for the study of crustal evolution. The genesis and dynamic background of the Late Triassic-Early Jurassic magmatism in this area are still controversial. To solve the above problems, this paper takes the Qieqiong syenogranitic granite in the middle south region of Lhasa terrane as a study. The object is analyzed by petrography, zircon U-Pb geochronology, Hf isotope and whole-rock geochemical characteristics, and its petrogenic characteristics and tectonic significance are discussed. Qieqiong syenogranitic granites is mainly composed of quartz, potassium feldspar, plagioclase and biotite. The U-Pb weighted mean age of magmatic zircon is 210.28±0.92 Ma (MSWD=0.99), which was formed in the Late Triassic. The rock is characterized by high SiO2 (73.44%~75.76%), high K2O (4.87%~5.15%) and high Al2O3 (12.58%~13.40%). The Al saturation index (A/CNK) is more than 1.0 and belongs to peraluminous high K calc-alkaline S-type granite. Light rare earth elements are relatively enriched and have moderate negative europium anomalies. Trace elements enrich K, Rb and radioactive elements U and Th of large ion lithophile elements, and deplete elements Ba, Nb, Sr, Ti, Zr and Hf in varying degrees. The εHf(t) was a lower negative value (-4.2 to -2.6), and the Hf two stage mode age was between 1262 Ma and 1347 Ma. The syenogranitic granites was formed in a post-collisional extensional tectonic environment and was the product of partial melting of argillaceous sediments in the crust. At the end of Middle Permian, collision orogeny occurred between the southern margin of middle Lhasa terrane and the northern margin of Australia, which resulted in the closure of the Songdo Tethyan Ocean and subsequent post-collision magmatism, forming the Late Triassic granite belt near the north latitude of Lhasa terrane at 30 degrees.