Abstract: In this paper, we performed comprehensive analyses on the monzonitic granite outcropped in the Qinmalong District, Nanmulin County, Tibet including field geological survey, petrology, LA-ICP-MS zircon U-Pb dating, elemental and Lu-Hf isotope geochemistry. The results showed that the monzonitic granite from the Qinmalong District belongs to the A-type granite and formed in the Paleogene (E1). The LA-ICP-MS zircon U-Pb age of the granite was 62.0±0.5 to 63.0±0.5 Ma. The weakly peraluminous monzonitic granite formed in high temperature (the saturation temperature of zircon was 745805 ℃, averaged at 766 ℃) and belongs to the high-potassium-calcium-alkaline series. It was enriched in SiO2 (72.6%74.97%), Na2O (2.86%3.59%) and K2O (4.12%5.25%) but depleted in CaO (0.72%1.39%) and MgO (0.26%0.36%). In addition, the granite had high FeOT/MgO value (7.2610.30) and obvious negative Eu anomalies (Eu/Eu*=0.400.70), depleted in Ba, Sr, P and Ti but enriched in Rb, Th, K, Zr and Hf element. The εHf(t) value was -4.7-1.8. The cursts two-stage Hf model age (tDM2) was 1.11.3 Ga. Our study indicates that the A-type granite originates from partial melting of the crustal materials in the Gangdese basement and formed in a tectonic setting of localized stretching in arc environment in response to the subduction and collision between the Indian and Eurasian Plates in the Paleogene.

Key words: monzonitic granite of Qinmalong District, zircon U-Pb dating, element and Lu-Hf isotope geochemistry, petrogenesis, Gangdese