Zircon U-Pb age, geochemistry and geological significances of the biotite monzogranite in Lhasa rock mass, Tibet

The Lhasa rock mass is a compound rock mass, locating in the eastern section of the Gangdise belt. Based on detailed geological survey, zircon U-Pb dating and geochemical studies on the biotite monzogranite in the Lhasa rock mass, it is believed that the Lhasa rock mass was formed during the main collision stage of the Indian and Asian continents. The U-Pb dating of zircons from the biotite monzogranite yields three ages, 57±0.5Ma,58±1Ma, and 59±1Ma, suggesting that the Lhasa rock mass is the product of paleocene magmatic activity. Geochemically, the representative biotite monzogranite in the Lhasa rock mass is of high SiO₂ (69.94%~76.62%), high alkali (6.95%~8.44%), and high CaO(0.68%~2.53%) compositions. Relatively, the biotite monzogranite in the Lhasa rock mass is rich in LREE and LILE such as Ba、Rb、Th and poor in HREE and HFSE such as Nb, Ta, P, and Ti, with an obvious Eu negative anomaly. All geochemical characteristics indicate that the Lhasa rock mass is a typical calc-alkaline I-type granite rock mass, which is favorable for skarn-typed metallogenic processes in the Gangdise belt.